Regarding the title of your question:

How can I kill a Frida server without root?

You can't, and fortunately, you don't need to, since you're on palera1n without root (iOS 16.7.10) → no root access → you can't kill system processes.

About “Error attaching: module not found in ‘/usr/lib/frida/frida-agent.dylib’”

This error means that you are using an old or rooted configuration of Frida, which searches in /usr/lib/, but in rootless everything is in /var/jb/

Possible solution:

Download the latest version of frida-server + frida-agent.dylib (iOS arm64e) from:
https://github.com/frida/frida/releases
Place both files in /var/mobile/ (this folder is yours, you don't need root)
Run your own instance of Frida:

chmod +x /var/mobile/frida-server
/var/mobile/frida-server --agent-path=/var/mobile/frida-agent.dylib -l 127.0.0.1:27043 &

Connect from your PC:

frida -H 127.0.0.1:27043 -U