I can launch the game and hear it start up, but the window is invisible. I can't view the game. I tried several Proton versions, 9, 8, 7, 6.3.8 and none of them fixed this. In all versions the game launched just fine and I could hear it, but not see it.

To be clear it isn't a black screen, the application simply has no window. So if I select it on my task bar or ralt-tab to it, nothing changes. I'm still able to browse the web for example. It's as if I did not alt-tab to the game at all. When viewing running applications, the preview to the game leaves space for a whole fullscreen application, but is invisible (not black, empty).