For me it started crashing frequently as well. But I tried it on my windows partition with the same result (and even more frequent crashes). So I thought it must be some update of the game that introduced that and not Proton/Linux.
Then I tried several Proton versions and one of the older ones seems to be crashing less so I can actually play for some time.
I think I Stück with 8. It has not completely solved the issue but I can at least play for half an hour before it crashes. No idea if it’s related to Proton at all or if I just got lucky.