This one is more of a bandaid than anything but have you tried using gamescope?
Also, for testing purposes you could see if you are able to run another X window manager and see if it is a problem with X rather than Wayland. dwm is very small and in the AUR, if you install that and xorg-xinit, you can jump over to a getty and create .xinitrc in your home folder with the line exec dwm and run startx. You’ll need dmenu as well to run things and that can also be found in the AUR.