If you’re comfortable with helping the Proton developers fix the issue, I‘d recommend searching Proton‘s Github issues for the game that won‘t run.
If your problem hasn‘t already been reported, create a proton log (run the game with the launch option PROTON_LOG=1 %command% once and find the log in your home directory). If an issue for the game doesn‘t exist already, you can open up a new one. Otherwise, append your log to the existing issue in a comment and describe what‘s happening exactly.
The devs over there are usually really helpful and nice. Many of my reports have been fixed within hours or days in bleeding-edge, although it can of course take longer if the issue is more complicated.