The only games that I really ever struggle with are ones that have anticheat. And EasyAntiCheat is going linux friendly so something like 95 of the top 100 games on steam will either work natively or via proton.
And with Valve pushing the SteamDeck is see that number going to 100 soon.
[1] https://github.com/GloriousEggroll/proton-ge-custom/releases