I don't have the slightest clue how to do anything with snapshots and it's been months since it began anyway so I wouldn't even know where to start

Well, if you didn't create any, you can't go back to them.

My suggestion is to find the archival ISOs of older versions and try them WITHOUT updating after installing them offline.

Though, if you end up having to install gamescope from the internet, then you're likely getting the exact same latest version no matter what distro you use.

Hence, maybe just easier to learn how to install older versions of packages on cachy. The Arch archive repo makes that quite doable.

And even if I did know which version caused the problem, I wouldn't know where to go from there.

You pin the package/system and prevent it from updating so it keeps working for you. And report the bug so it can be fixed.

All of this stuff is a community effort. You can wait for someone else to figure out the problem of course, but the fastest solution is usually to volunteer yourself.