This is the vanilla game.

The game would crash to desktop after the end of City Escape, after the score count up, at the moment it would show the first achievement / say "saving game". This is regardless of being full screen or windowed.

I had to set the launch command to PROTON_USE_WINED3D=1 %command% and then it ran fine with proton 9.0-3 (successfully completed the first level, then the next one, then chao garden shenanigans; save seems to work).