I don’t know if they support the OG Steam OS anymore, and if they do, it’s not going to be a good experience for regular desktop use. Steam Deck is Arch based, and I think there’s where their efforts are going these days.
That said, if you want something with a nice out of the box experience for gaming, consider Nobara Linux. It’s based on Fedora and maintained by the person who does the Proton-GE releases (Glorious Eggroll), which have fixed that aren’t in the official Steam Proton releases (e.g. fixes for specific games that haven’t landed yet). It should be a pretty good experience.
However, just installing Mint Debian edition should work fine, you’ll just need to make sure you get the right drivers and that’s about it.