Blind guess that your issue is https://gitlab.freedesktop.org/mesa/mesa/-/issues/3969.
I think you hit the nail on the head @kisak-valve, that looks like it. I see a patch was done today so I'll wait for a Mesa update and hopefully that will fix it and make this game compatible again. Thanks for the quick response!
Update to Mesa 21.0.3-3 on Arch Linux includes the patch from the issue you linked to. After updating the immediately runs again so I think I can close this? Thanks for your quick pointer to the right suspect.
Nothing extracted yet.
Compatibility Report
System Information
I confirm:
steam-206020.log
Symptoms
After clicking to play the game a black window opens which then resizes to full screen and instead of the game load screen appearing it immediately crashes. I take it this happens when it tries to switch to 1024x768 resolution in 16 bit color. That's the only resolution the game works on and it can't play in a window.
The game worked fine with Mesa 20.3.4 but after upgrading to Mesa 21 it crashes as described.
Reproduction
After downgrading to Mesa 20.3.4 the game will play again.
Update: upgrade to Mesa 21.0.3-3 includes fix for the issue that caused the game to stop working with Steam Play.