Ganes you can't play under the native steam os are basically all multiplayer titles with anti cheat. So Fortnite, Destiny 2, CodWarzone don't work UNESS you install windows 10 or 11.

Some multiplayer games however that did not used to work under steam OS got updated at some point and now do. Apex legends, division 2 for example.

I think some of the confusion comes from old articles still out there saying this or that doesn't work when it's been updated since then. Basically your best bet is to just look up specific games you are curious about and see how they run.

Even demanding single player games have been updated like Cyberpunk which is now deck verified and has its own graphics setting preset in the game.