Description:

After dispatch workspace , if both source and origin workspaces contains tabbed layoutts, the tab bar from WS1 is rendered, then immediately replace by the tab bar from WS2, and back again. This produces a very noticeable flicker.

Look like the oscillation rate depends on the redraw rate of wayland. Slow when nothing is going on, faster if there's a video playing, etc'.

Reproducible:
100% here.

Repro:
hyprland.conf: input:follow_mouse = 0

Setup tabbed layouts on two workspaces, say 1 and 2.
Switch to 2, then back to 1 again and this happens.

It only seems to happen if no focus event, such as clicking a window, happens after switching to 2 and before switching back to 1. If you click a windows afetr switching then switch back, it doesn't trigger.

Workaround:
use a shell script for switching, and add a hyprctl dispatch hy3:changefocus bottom at the end to force a focus event after switching. Nothing special about bottom, it just causes the least visual jank.

Here's the script I use, which also replicates sway's "back-and-forth" feature.

hypr_switch_workspace.sh

#!/bin/bash

# Define the workspace name from the script's argument
TARGET_WORKSPACE=$1

# Use hyprctl to get the active workspace name
ACTIVE_WORKSPACE=$(hyprctl activeworkspace -j | jq -r '.name')

# Check if the requested workspace is already active
# for comparison , strip optional "name:" prefix
if [ "${TARGET_WORKSPACE##name:}" == "$ACTIVE_WORKSPACE" ]; then
  # If it is, switch to the previous workspace
  hyprctl dispatch workspace previous
else
  # Otherwise, switch to the requested workspace
  hyprctl dispatch workspace "$TARGET_WORKSPACE"
fi

# workaround flicker when changing workspace
hyprctl dispatch hy3:changefocus bottom

and

bind = $mod, 1, exec, ~/.config/hypr/scripts/hypr_switch_workspace.sh 1

etc'

The workaround does not work when moving to an empty workspace, since there is nothing there to generate a focus event with.
Another corner case is when switching to a workspace a moment before a notification appears, where the same flashing tab bar phenomena can sometimes still trigger.