

Flawless on Proton 9

Works flawlessly out of the box.
Would a typical gamer enjoy it, though...? I didn't. Played with Steam Controllerset to mimic keyboard (WSAD).

Keep in mind that DOASPJ isn't the most stable game on Windows. All the stability issues I found on the Steam Deck are ones common to the Windows version, so it runs pretty much on par with its intended hardware. I do recommend locking the FPS to 30 as that'll be more stable than the constant drops from mid-50s to low-40s and, in some cases, 30. This isn't the kind of game where playing at 60 FPS makes any difference gameplay-wise anyway.
Changed R4 to left mouse click and right trackpad to mouse.
There's a launch window before the game starts that requires mouse controls to use.
On a certain weekday when there's many NPCs on screen, the game slows down but it's still playable,
Works very well once you get it started. Works with a controller right away once you get past the launch window. Might require changing controls in the Steam menu if you don't like the given button layout.
Runs better than Windows!
I tried playing on a different version of Proton a while back which had a bug where you couldn't get achievements; but now it works pretty much perfectly in all respects! If you've had trouble before, definitely try again now!
Clashing textures

I noticed some texture z-fighting but due to the lo-fi graphics of the game I can't tell if it's a bug or just part of the aesthetic. Also game-pad doesn't work.

I though it was borked but I got it to work with "PROTON_USE_WINED3D11=1 %command%" in the launch option, anyway my controller doesn't work, and I can't get it to rebind my key to azerty keyboard, and I have FPS drop when I move the camera too much

I get a message box saying the game crashed