Also, here is a screen recording showcasing the bug, just in case: https://files.catbox.moe/ouu7mf.mkv (had to upload it to an external site since github doesn't support mkv)
The game launches fine on my side without the need to manually fullscreen it, behaved the same on proton 9.0-4 and experimental. In your case, it appears that the game is failing to render at all until you switch modes. The xrandr error in your log is likely a symptom of the issue, but it's hard to know what might be the root cause. Maybe updating your kernel and nvidia driver will fix it, maybe running xrandr will show some funky resolution listed.
There's a low fps/lag issue on the 3rd room of the game (the one with the cat)
This one
The same issue happens with wine as well. There is other people claiming to have the same issue on protondb so it's somewhat reproducible
proton 9.0-4x1 2025-01
Compatibility Report
System Information
I confirm:
Proton Log
steam-814540.log
Symptoms
The game just starts off in a black window with sound, until I press Alt+Enter to force the game into fullscreen.
Reproduction
Not sure exactly, my sincere apologies.