Artifacting would occur when scoutflies were visable. Tried Proton Experimental and 9.0-4, but it seems to have resolved when switching to an older version (7.0-6).

I use a contoller when playing. Steam thinks the game is still open when quitting via the game's menu and locks my mouse in desktop, rending it completely unusable. Shift-Tab to Steam Overlay and exitting the game has been a reliable workaround. Not sure what is causing it.