Works flawlessly in here too. Steam info.
Also works flawlessly for me.
Not flawless here, though the issue I see is minor. The 'would you like to quit?' dialog box is empty and I had to guess which is 'quit'.

Also somewhat choppy when playing windowed.
I see no difference in fullscreen vs windowed with my system. Empty dialog box appears only when using window manager to close game window, quitting from game menu works normally both fullscreen and windowed. Proton 4.11-11, game version 1.1.2, Steam Info.
Doesnt for me in either. I should add that I was getting the error fullscreen or windowed, I just windowed it so I could take that snap easier. Who knows, maybe it doesn't like KDE as much (what Im using).
Switching from Fullscreen to Windowed mode is broken. When the user switches to Windowed, the game becomes unresponsive, and the content in the window remains scaled as if it were still in fullscreen. The game must then be force-quit or quit via Steam. Essentially, the game is stuck in fullscreen.
Proton version: Experimental
steam-838310.log
System: https://gist.github.com/nightsky30/df2dee0a051109899521b8f549a199e2
proton 4.11-11x1 2020-01
Works flawlessly.
My Steam info