Almost perfect, except the fullscreen issue.
The game initially starts in fullscreen mode, but, upon switching to windowed mode, it does not successfully switch back to fullscreen.
First try starting it just opened a black frozen screen, second time it worked fine. Occasionally randomly throws script errors (not related to exiting and entering the game) but simply restarting the game fixes it (happened to me 3 times in 3 hours of playtime).
Apart from the occasional "script errors", everything seems fine
Going back to the main menu and then continuing causes a bunch of "script errors", but game play seems not to be impacted. This can be avoided by exiting the game and starting it again...
5.8-GE-2-MF GloriousEggroll
AUR proton-ge-custom-bin 5.8_GE_2_MF-1
switch worked fine, but continuing gameplay resulted in a crash when loading level, restart of game allowed gameplay to continue.
occasional script errors on some game screens
Crashes at startup