If you aren't playing games with a kernel anti cheat, legit 99.99% of games will work. Nearly every broken game is due to an anticheat. ProtonDB lists only 4% of the top 1000 Steam games as "borked", and the majority of those are due to anticheat. Any that aren't will likely be fixed by Proton updates.

If you also want to avoid any games that might not be super smooth, filtering Bronze ranked games are another 3%. Silver is another 8%, but I've never had an issue running a Silver rated game.