Proton isn’t an emulator; It’s a compatibility layer. All it’s doing is taking the Linux<>Windows stuff and converting back and forth. There’s very little efficiency loss, (and some games even run better because Linux tends to be a lighter OS.)

The big issue with Linux is anticheat. Some of the largest anticheat companies have chosen not to support Linux, or the game devs have disabled Linux support on their end. But to be clear, that’s not a choice Linux has made; It’s a choice the game devs made to exclude Linux players, because they want kernel-level control which Linux won’t allow.

Gaming on Linux used to be a big hassle, as it basically required devs to write a native Linux version of the game. But nowadays Proton does that translation for them, and is so lightweight that it’s negligible. If you have any doubts, check out protondb, which is a published list of game compatibility ratings. Gold will play just fine in 90% of cases. Platinum is going to be seamless. Native means there’s a specific Linux version. And Steam Deck Verified simply means the devs have set specific controller/aspect ratio/frame rate/etc settings for when the game is booted on a Steam Deck. Even if it’s not SD Verified, the rating will tell you whether or not the game will boot and run.