@face
Thanks for the fix!
Just a reminder to myself and others who might encounter the same:
After enabling and starting sys-gui-gpu my wireless mouse didn’t work anymore although it was recognized.
I ran the command for creating my sys-usb again, in my case
sudo qubesctl state.sls qvm.sys-usb
and there was a total of 9 states run with 2 changes.
After that I removed my USB receiver and plugged it in again and the mouse is working again.