This is a expected behaviour from salesforce when feed tracking is enabled for cases or work orders, the
page-level action menu on those records contains only custom buttons and supported standard buttons.
Quick actions appear on the Chatter tab.
So in order to not see the action in feed, you need to disable the feed tracking for your case object.
Steps are:- setup--> feed tracking--> select case--> disable it and save
Update
In winter 21, You can actually do this using Lightning App Builder dynamic actions. Upgrade your page to
dynamic actions and add the quick actions using lightning app builder. It will come in highlight panel even
if feed tracking is enabled.
Set Up and Maintain Collaboration Tools
Help your users collaborate with each other and with people outside your organization. For help with basic Salesforce
administration, see Set Up Your Organization.
       Salesforce Chatter
        Connect, engage, and motivate users to collaborate and work efficiently across the organization regardless of their role
        or location.
Salesforce Chatter
Connect, engage, and motivate users to collaborate and work efficiently across the organization regardless of their role or
location.
REQUIRED EDITIONS AND USER PERMISSIONS
Available in: Salesforce Classic (not available in all orgs)
Available in: Essentials, Group, Professional, Enterprise, Performance, Unlimited, Contact Manager, and Developer Editions
USER PERMISSIONS NEEDED
To enable Chatter:                                                              Customize Application
Salesforce Chatter lets users collaborate on sales opportunities, service cases, campaigns, and projects with embedded apps and
custom actions. By default, Salesforce organizations created after June 22, 2010 have Chatter already enabled for all users.
However, if you want Chatter to be available to a limited group of people in your org, you can do a profile-based rollout instead.
With a profile-based rollout, only users who have been assigned the required user profile or permission set have access to
Chatter. A profile-based rollout is useful for larger companies and companies or government agencies with regulatory
constraints. It allows such orgs to plan a controlled deployment on a department-by-department basis.
Although we recommend an org-wide Chatter deployment, the option to limit its availability is there. Ask Salesforce about
enabling a profile-based Chatter rollout. Chatter is secure and works in accordance with all the security and permission settings
in your Salesforce organization.
       Profile-Based Chatter Rollout Overview
        A profile-based rollout of Chatter makes Chatter available to a controlled set of users instead of all users in your
        organization.
       Encryption for Chatter
        Encryption for Chatter lets you encrypt sensitive data when it’s stored, and not just when it’s transmitted over a
        network. As of the Winter ’18 release, mass encryption and decryption of Chatter data is generally available. To enable
        encryption for Chatter, contact support for help with setting it up.
       Chatter Settings
        In Salesforce and the Salesforce mobile app, Chatter is enabled by default. Configure various Chatter features and
        customize the Chatter experience for your users on the Chatter Settings page in Setup.
   Publisher Actions and Layouts
    Actions add functionality to the Chatter Publisher in Salesforce Classic. Actions let your users do more in Salesforce
    across all devices.
   Enable Code Snippets and Assign Permissions to Use Them
    Use code snippets to enter syntax-highlighted code samples through the Chatter publisher. To make code snippets
    available, enable them and assign the permission to use them. There are two ways to enable code snippets and assign
    permission: through a user profile (step 1) or through a permission set (step 2). Code snippets are available in Lightning
    Experience and Experience Builder sites that are based on the Customer Service template.
   Assign Pin Post Permission
    Pin your most critical information to the top of a feed. In group and topics feeds, when someone posts critical
    information, an authorized user can pin that post to the top. Pin up to three posts. Each post stays in place until an
    authorized user unpins it. After you enable post pinning through Chatter Settings, you can assign the Pin Posts in
    Feeds permission through a permission set or a user profile.
   Feed Tracking
    Feed tracking detects changes to tracked record fields and posts them as updates in the What I Follow feed. Users who
    follow a record, see those updates in their view of What I Follow, with one exception. Updates users make themselves
    aren’t posted to What I Follow. Users can see those updates in their profile feeds.
   Chatter Email Settings and Branding
    Chatter email settings let you change the format of your company’s outgoing emails and control whether users receive
    email notifications.
   Chatter Post Actions and Layouts
    Actions on posts and comments appear in the drop-down menu on a post or comment. Users can edit, bookmark, mute,
    and delete posts, add topics, and create tasks from posts.
   Group Layouts
    The group layout lets you customize which fields, buttons, actions, and lists appear in Chatter groups. Changes to the
    group layout affect all groups in your organization, but they appear only on the group pages in the Salesforce mobile
    app. Changes to the group publisher appear in both the full Salesforce site and the Salesforce mobile app.
   Topics for Objects
    Topics for objects offers a powerful way to crowdsource your company's key themes and issues. Users can add topics
    to records to organize them by common themes.
   Customize Chatter Influence
    Customize activity thresholds for posts, comments, and likes to improve the Chatter influence calculation.
   Allow Users to Thank Their Coworkers
    Recognize your coworkers with thanks badges and post your thanks directly to the Chatter feed.
   Guidelines for Deleting Your Users’ Chatter Messages
    Salesforce administrators with the Manage Chatter Messages permission can access all users’ private messages via
    SOAP API. You can view and delete any message (for example, for compliance).
   Report on Chatter with the Dashboards Package
    The Chatter Dashboards package for Salesforce Classic packs a punch! You get multiple dashboards, over 100 reports,
    and even custom report types. Use the dashboards to monitor and manage Chatter adoption and engagement in your
    organization.
   Chatter Desktop
    Control access to Chatter Desktop and install and configure the Chatter Desktop Managed Version.
Profile-Based Chatter Rollout Overview
A profile-based rollout of Chatter makes Chatter available to a controlled set of users instead of all users in your organization.
REQUIRED EDITIONS
Available in: both Salesforce Classic (not available in all orgs) and Lightning Experience
Available in: Enterprise, Performance, and Unlimited Editions
Once profile-based rollout is enabled for your organization, you can enable Chatter for the users with the required user profile
or permission sets. Users without the right profile or permission set don’t have access to Chatter.
EXAMPLE Let’s say you assign a profile or permission set that excludes Chatter access to a subset of users. These users still
have access to Salesforce objects, but they don’t see the record feed and they can’t post or comment.
        Get Ready for Profile-Based Rollout of Chatter
         If you’re rolling out Chatter to a subset of your users, you can manage Chatter access with custom user profiles and
         permission sets. There’s a little up-front work you can do to prepare.
        Control Chatter Access Through User Profiles
         Modify existing custom user profiles to allow or deny access to Chatter.
        Control Chatter Access Through Permission Sets
         Manage Chatter access by modifying existing permission sets or setting up new ones.
        Profile-Based Rollout Considerations
         In organizations that use Chatter profile-based rollout, limitations apply. There are limits with user profiles,
         permissions sets, and the interaction between users with and without Chatter access.
Get Ready for Profile-Based Rollout of Chatter
If you’re rolling out Chatter to a subset of your users, you can manage Chatter access with custom user profiles and permission
sets. There’s a little up-front work you can do to prepare.
REQUIRED EDITIONS
Available in: both Salesforce Classic (not available in all orgs) and Lightning Experience
Available in: Enterprise, Performance, and Unlimited Editions
From a high-level perspective, a profile-based rollout of Chatter consists of these steps:
NOTE Before you begin, disable Chatter for your entire organization (in Setup, go to Chatter settings and deselect Enable).
    1.   Salesforce enables the Chatter profile-based rollout feature for your organization.
    2.   You determine who gets access to Chatter.
    3.   You review and modify existing custom user profiles and permissions sets.
    4.   Verify that, in a custom user profile or permission set, the Enable Chatter,permission has the desired setting.
    5. To allow or restrict Chatter access, assign the associated profile or permission set to users.
    6. You turn on Chatter for your organization.
         NOTE Perform step 6 as a separate, final step. If step 6 is combined with another step or performed out of order,
         unpredictable and undesirable results can occur.
Control Chatter Access Through User Profiles
Modify existing custom user profiles to allow or deny access to Chatter.
REQUIRED EDITIONS AND USER PERMISSIONS
Available in: both Salesforce Classic (not available in all orgs) and Lightning Experience
Available in: Enterprise, Performance, and Unlimited Editions
USER PERMISSIONS NEEDED
To enable Chatter:                                                                   Customize Application
When Salesforce turns on Chatter profile-based rollout for your organization, it adds the Enable Chatter permission to your existing
user profiles and permissions sets. Enable Chatter is automatically enabled for all standard profiles. It’s also automatically enabled for
custom profiles when any of these user-level permissions are enabled manually or as part of a license:
        Create and Own New Chatter Groups (ChatterOwnGroups)—Users with this permission can create groups in Chatter.
        Create and Share Content Deliveries for Chatter Files (ChatterFileLink)—Users with this permission can use files with
         Chatter, like uploading, attaching, and sharing.
        Invite Customers To Chatter (ChatterInviteExternalUsers)—Users with this permission can invite users who don’t have
         a Salesforce license to Chatter.
        Manage Chatter Messages and Direct Messages (ManageChatterMessages)—Users with this permission have
         management access to Chatter Messages and Direct Messages (Experience Builder sites).
        Moderate Chatter (ModerateChatter)—Users with this permission can moderate Chatter feeds.
        Moderate Chatter Feeds (ModerateNetworkFeeds)—Users with this permission can moderate feeds in sites.
        Use Case Feed (ViewCaseInteraction)—Users with this permission can access Case feeds.
        View All Data (ViewAllData)—Users with this permission can view all data, regardless of their membership status in a
         feed or ownership of a record.
Modify your existing custom profiles with the desired permissions to manage access to Chatter, and create custom profiles, if
necessary.
    1. Log in as a Salesforce administrator.
    2. From Setup, enter Profiles in the Quick Find box, then select Profiles.
3. For each custom user profile:
       a. Click Edit.
       b. In the Administrative Permissions section, select or deselect Enable Chatter, depending on whether you want
           users with this profile to have Chatter access.
            IMPORTANT The Enable Chatter permission is available only if Chatter profile-based rollout is enabled for
            your organization. Salesforce enables profile-based rollout at your request. After profile-based rollout is
                  enabled, selecting the Enable Chatter permission on a profile doesn't automatically enable Chatter for people
                  with that profile. People can't use Chatter until you turn on Chatter for your organization.
            c. Save your changes.
    4. If applicable, create custom user profiles with the desired permissions and assign them to users.
Control Chatter Access Through Permission Sets
Manage Chatter access by modifying existing permission sets or setting up new ones.
REQUIRED EDITIONS AND USER PERMISSIONS
Available in: both Salesforce Classic (not available in all orgs) and Lightning Experience
Available in: Enterprise, Performance, and Unlimited Editions
USER PERMISSIONS NEEDED
To enable Chatter:                                                                  Customize Application
When you enable or disable Chatter through permission sets, consider that:
        When you enable Chatter in a permission set, the permission set takes precedence over user profile settings. All users
         with a Chatter-enabled permission set have access to Chatter, even if Chatter isn't enabled in their user profile.
        When you disable Chatter in a permission set, the permission set doesn't take precedence over user profile settings. All
         users with a Chatter-enabled user profile have access to Chatter, even if Chatter is disabled in their permission set. To
         prevent that person from accessing Chatter, disable Chatter in both the person's user profile and permission set.
        When Chatter profile-based rollout is enabled for an org, Chatter is automatically enabled when some user-level
         permissions are already enabled. And some Chatter settings are disabled. For more information, see Profile-Based
         Rollout Considerations.
Verify that existing permission sets include the correct and required Chatter permissions for the desired subset of users.
    1. In Setup, navigate to Permission Sets.
    2. For each existing user-level permission set:
           a. In the System section, click System Permissions.
           b. Click Edit, and select Enable Chatter. The Enable Chatter permission is available in a permission set only
               after Chatter profile-based rollout is enabled for your org.
            c. Save your changes.
    3. If applicable, create permission sets with the desired permissions and assign them to users. By default, all permissions
       in a new permission set are disabled. Enable the appropriate permissions in the new permission set to give users access
       to Chatter plus extra levels of management authority.
                Create and Own New Chatter Groups (ChatterOwnGroups)—Users with this permission can create groups in
                 Chatter.
                Create and Share Content Deliveries for Chatter Files (ChatterFileLink)—Users with this permission can use
                 files with Chatter, like uploading, attaching, and sharing.
                Invite Customers To Chatter (ChatterInviteExternalUsers)—Users with this permission can invite users who
                 don’t have a Salesforce license to Chatter.
                Manage Chatter Messages and Direct Messages (ManageChatterMessages)—Users with this permission have
                 management access to Chatter Messages and Direct Messages (Experience Builder sites).
                Moderate Chatter (ModerateChatter)—Users with this permission can moderate Chatter feeds.
                Moderate Chatter Feeds (ModerateNetworkFeeds)—Users with this permission can moderate feeds in sites.
                Use Case Feed (ViewCaseInteraction)—Users with this permission can access Case feeds.
                View All Data (ViewAllData)—Users with this permission can view all data, regardless of their membership
                 status in a feed or ownership of a record.
NOTE Selecting the Enable Chatter permission in a person's permission set doesn't automatically turn on Chatter for that
person. People can't use Chatter until you turn on Chatter for your organization.
Profile-Based Rollout Considerations
In organizations that use Chatter profile-based rollout, limitations apply. There are limits with user profiles, permissions sets,
and the interaction between users with and without Chatter access.
       The Enable Chatter option isn’t available on profiles or permission sets unless profile-based rollout of Chatter is enabled for
        the organization.
       When you enable Chatter in a permission set, the permission set takes precedence over user profile settings. All users with a
        Chatter-enabled permission set have access to Chatter, even if Chatter isn't enabled in their user profile.
       When you disable Chatter in a permission set, the permission set doesn't take precedence over user profile settings. All users
        with a Chatter-enabled user profile have access to Chatter, even if Chatter is disabled in their permission set. To prevent that
        person from accessing Chatter, disable Chatter in both the person's user profile and permission set.
       Enabling Chatter in a person's user profile or permission set doesn't automatically turn on Chatter for the organization.
        Turn on Chatter for your organization in Setup, after you modify user profiles and permission sets.
       Standard Salesforce user profiles have Chatter enabled by default. You can’t disable Chatter for these standard profiles.
       Don't deselect the Enable Chatter permission on a cloned Chatter External user profile. The user sees an error message and
        can’t log in.
       Don’t deselect the Enable Chatter permission on a cloned Chatter Free or Chatter Moderator profile. You get an error
        message and can’t save the profile.
       Enabling Chatter and profile-based rollout for an organization also enables a set of dependent Chatter user permissions. If
        Chatter is disabled for the organization, these permissions are also disabled at the same time. However, if Chatter is
        reenabled, these permissions aren’t automatically re-enabled, and the administrator must enable them explicitly.
       When profile-based rollout of Chatter is enabled for an organization, Chatter is automatically enabled for standard profiles.
        For custom profiles and permission sets, Chatter is automatically enabled if any of these user-level permissions are enabled
        manually or as part of a license:
            o Create and Own New Chatter Groups (ChatterOwnGroups)—Users with this permission can create groups in
                 Chatter.
            o Create and Share Content Deliveries for Chatter Files (ChatterFileLink)—Users with this permission can use
                 files with Chatter, like uploading, attaching, and sharing.
            o Invite Customers To Chatter (ChatterInviteExternalUsers)—Users with this permission can invite users who
                 don’t have a Salesforce license to Chatter.
            o Manage Chatter Messages and Direct Messages (ManageChatterMessages)—Users with this permission have
                 management access to Chatter Messages and Direct Messages (Experience Builder sites).
            o Moderate Chatter (ModerateChatter)—Users with this permission can moderate Chatter feeds.
            o Moderate Chatter Feeds (ModerateNetworkFeeds)—Users with this permission can moderate feeds in sites.
            o Use Case Feed (ViewCaseInteraction)—Users with this permission can access Case feeds.
            o View All Data (ViewAllData)—Users with this permission can view all data, regardless of their membership
                 status in a feed or ownership of a record.
       When profile-based rollout of Chatter is enabled for an organization, two org preferences are set to OFF:
            o Allow Coworker Invitations (inviteCsnUserEnabled)
            o Allow Customer Invitations (inviteChatterGuestEnabled)
       In organizations that have thanks badges enabled, users with access to Chatter can’t thank users who don’t have access to
        Chatter.
       If your organization already has Chatter enabled and switches to profile-based rollout of Chatter, manually enable Chatter in
        all existing custom profiles and permission sets. Otherwise, users that are assigned these custom profiles and permission sets
        lose access to Chatter.
       When profile-based rollout of Chatter is enabled in Salesforce Classic, users who can’t use Chatter also can’t use global
        search. Advanced search is available to these users.
Feed Tracking
Feed tracking detects changes to tracked record fields and posts them as updates in the What I Follow feed. Users who follow a
record, see those updates in their view of What I Follow, with one exception. Updates users make themselves aren’t posted to
What I Follow. Users can see those updates in their profile feeds.
REQUIRED EDITIONS AND USER PERMISSIONS
Available in: both Salesforce Classic and Lightning Experience
Available in: Essentials, Group, Professional, Enterprise, Performance, Unlimited, Contact Manager, Developer, and Database.com Edit
The Account, Case, Contact, Lead, Opportunity, and User objects are not available in Database.com.
Salesforce Connect external objects are available in: Developer Edition and for an extra cost in: Enterprise, Performance, and Unlimited Edit
USER PERMISSIONS NEEDED
To select the fields to track:                                                                      “Customize Application”
To view the field tracking setup page:                                                              “View Setup and Configuration”
Feed tracking is available for record fields. You can configure feed tracking for users, Chatter groups, topics, custom objects,
external objects, and the following standard objects: accounts, article types, assets, campaigns, cases, contacts, contracts,
dashboards, events, leads, opportunities, products, reports, solutions, and tasks.
NOTE In Lightning Experience, most object records don't show a Chatter tab unless Feed Tracking is enabled for the object.
Exceptions include Group, Site, and User objects.
Sharing rules and field-level security determine the visibility of record changes in Chatter feeds. To see changes to a record in
their feeds, users must have access to the record.
These objects and fields are tracked by default:
        Account: Account Name, Account Owner
        Case: Case Owner, Priority, Status
        Chatter Group: Allow Customers, Description, Group Access, Information Body, Information
         Title, Name, Owner Name
        Contact: Account Name, Contact Owner, Name
        Lead: Lead Owner, Lead Status, Name
        Opportunity: Amount, Close Date, Opportunity Name, Opportunity Owner, Stage
        Topic: Description
        User: About Me, Address, Email, Manager, Phone, Title
Tracked feed updates that are older than 45 days and have no likes or comments are deleted automatically. The tracked feed updates
no longer appear in the feed. However, if auditing is enabled for a tracked field, the tracking field audit history is still available.
NOTE Reports on feed activities don’t include information about system-generated posts, such as feed tracked changes.
Tracked changes in a feed can be bundled together for quick and easy reading. This image shows two tracked change
notifications bundled together. On this record, Bat Chad changed the values for the Product Owner and QA Engineer fields.
       Customize Chatter Feed Tracking
        When you enable feed tracking for objects and records, users see updates for the objects and records that they follow in
        their What I Follow feed. Many objects and fields are tracked by default, but you can further customize feed tracking to
        include or exclude specific objects and fields.
       Feed Tracking Limitations
        Here are some limitations on tracking objects, fields, and topics.
       Feed Tracked Change Bundles
        We save you time and space in your feeds by bundling multiple feed tracked change updates into a quick-reference list.
        Bundles are collections of feed tracked change items that you see in feeds. You can see bundles in your browser. In
        Salesforce for Android and Salesforce for iOS, bundles appear only in record feeds.