Aspect Ratio has been forced to 16/9 in order to stop the second menu from breaking.
Steamdeck/Proton users should now not run into any issues.
Boss 3 side shots have now been nerfed in normal mode, speed remains the same in Harder difficulty
If the bug with Steamdeck persists, and that the second main menu doesn't function, please inform me about it and I'll do my best to try to repair it.
Thank you for your patience! Sorry for any inconvenience!