Linux

Well the Steam Deck's OS is forked from Arch so.

I play mostly Indie so I couldn't speak for stuff like anti-cheat/graphics but... the types of game I play, for the most part "it just works".
If you're into RPG maker games, they sometimes require workarounds (hint: you can hot-swap the contents of RPG Maker MV/MX/MZ into Linux's native nwjs...)
I think the only games that struggle on my computer are mostly because of GPU (I'm on a laptop) rather than anything else Tbh