if you're trying to get the game to run with mods using SAModManager, here's a couple finicky things I had to get right for it to work properly:

• SAModManager.exe needs to be in the game install dir, i.e. next to sonic2app.exe
• when running the mod manager, run it through protontricks against SA2, i.e. protontricks-launch --app-id 213610 SAModManager.exe
• you will need to install .net 8 (or newer if you're reading this later) in the prefix for this to work, when you try to launch samodmanager without it it should give you a download link, just download that and install it with the same protontricks-launch invocation above
• just run sa2 through steam once you have the modloader and mods installed, wasnt working through the mod manager itself but thats probably fixable im just lazy