

Out of curiosity, what happens if you try to run gamescope from the terminal to just run anything (not even having proton in the mix).
For example:
gamescope -f -W 2560 -H 1440 -r 144 --force-grab-cursor --mangoapp – glxgears
If this doesn’t run, you should get some log lines at least to let you know whats on fire with gamescope.
Well sorry. If it works for glxgears there is probably some other weird interaction happening with Steam + Gamescope + Game launching. (you could try to add glxgears as a non steam game to further push the boundaries of if anything will run from steam).
I don’t have an nvidia GPU so I couldn’t even possibly comment on the state of that situation, but I wish you the best of luck.