So steam play was already enabled, it looks like it defaults to "steam Linux runtime 1.0 (scout). When I select different versions of proton runtime I get different behavior dependig on which one I select.
Proton 9 says that it cannot switch to my monitors resolution,
Proton experimental and hot fix launch the game (I can hear it!), but things are ... Weird. It only renders the windows behind it and the custom game cursor. When I alt enter to bring it into Windows mode, it's still just the windows/desktop that would be behind the game but now it's scaled differently.
EDIT:
It's hard to tell but the above screenshot is the game window
Well I've installed BG3 just for the sake of testing and the DX11 launch results in a black screen. The Vulkan launch options crashing immediately...
Here is my steam logs when launching KSP I think the only thing of interest is this: