I don’t like playing in online mode because of the degraded performance, and all of my mods also will crash my game. I can only play custom maps in online mode and its driving me nuts. The game will abruptly crash mid loading screen on any map everytime without fail. I have tried changing proton versions to no avail, validating and reinstalling didnt work either.
I’m surprised you can play custom maps online because for me, any zombies map, custom or not, will crash my game. This is a known issue here. Since you only play offline I’d suggest installing the boiii client which fixes this crash as well as some other stuff.
This issue is also being mentioned on the proton GitHub page for this game so some people do know about it but whether or not it can/will be fixed by Valve is not known.