I have read these before

Then why didn't you mention that in the OP? It would have stopped both of us wasting our time. Please explicitly list *everything* else you've tried.

I would recommend removing xserver-xorg-video-intel but maybe I should stop bothering with this thread...

What is the graphics hardware and driver?

00:02.0 VGA compatible controller [0300]: Intel Corporation Iris Plus Graphics G1 (Ice Lake) [8086:8a56] (rev 07)
	Subsystem: Hewlett-Packard Company Device [103c:85f3]
	Kernel driver in use: i915
	Kernel modules: i915
00:04.0 Signal processing controller [1180]: Intel Corporation Device [8086:8a03] (rev 03)

No errors, it reports either mesa or software rendering, but with both the mouse is the same.

Renderer: OpenGL (Intel // Mesa Intel(R) UHD Graphics (ICL GT1) // 4.6 (Compatibility Profile) Mesa 20.3.5)
Renderer: Software (Cairo)

Thanks, I have read these before and it's unrelated unfortunately.

lspci -knn | grep -iA3 'vga\|3d\|display'

If you start the game from a terminal does it show any error messages?

I searched the interweb for you (you're welcome) and found these:

https://steamcommunity.com/app/239030/d … 769700617/

https://steamcommunity.com/app/239030/d … 415375714/

The problem isn't the same but it might be worth trying the posted solutions to see if they help.

I'm using i3wm and no desktop manager.
When I play the game "papers please" my mouse will hang about every 10s for 1s. outside of the game window, it works fine.

I does not matter whether the game uses mesa or software rendering.
It is the same for my touchpad as well as a usb mouse.
It does not matter whether I run compton or not.

I have played this game on another i3wm devuan setup and it worked fine. This does not seem like a common problem for this game.

Any idea or hints how I could find the cause of this?
Thanks a lot in advance!