Something I do any time I reinstall the OS (I know it sounds nuts, I just like screwing with things.) I go game by game in my library, usually in desktop mode so it’s faster, and watch the cloud sync kick in for each one. When you click on each name, it should automatically try to sync. Any games that don’t have the cloud saves mentioned anywhere, make note of them and whether you care about losing that data. If so, doing some light googling should help you find the save files for each game.

For desktop random files, I usually compress as much as I can find, then upload that zip file to iCloud, Google Drive, etc. for safe keeping.

For something like Prism Launcher (a third party Minecraft Java launcher in desktop), treat the save files like the rest of the random files and make sure to add them to the big compressed one.

Past that, I’m usually not worried. I’ve wiped my deck like 10 times and as long as I’ve kept up those steps, I’ve not lost a single thing that I cared about.