I switched to full time gaming on Linux (Arch) about six months ago. It is very good, and improving, though it will still often require tinkering (ProtonDB is very good for user reports). And certain games, like those with "kernel anti-cheat", probably won't work at all, indefinitely.

I can say that if you stick to Steam Deck Verified games, you will have very few problems; and if you enable compatibility (Proton) for non-Verified games, then almost every game will work, possibly with some tinkering.

I'm less familiar with non-Steam games, though I know Proton is not intended to be used outside of Steam. I guess that gaming outside of Steam would require more tinkering.