Depends on the game/publisher. Depending on the anticheat it can be as simple as enabling Linux/Proton support on the dev's side with a flag.

I can't play Destiny 2 with my Destiny obsessed friend, that's about all I've been impacted. Didn't really get into it anyway. I don't even check ProtonDB anymore before buying new games, they almost all work flawlessly these days.

Not quite, steam now installs EasyAntiCheat for linux when you first setup steam for instance. The games you will struggle with are games such as those published by Riot, some view that as a bonus though 😅

Counter-strike works, as do all valve titles. Overwatch, Splitgate and Titanfall work as well and so do most "non-real-time games", like Trackmania. Riot's games and Rainbow don't work. Check protondb for the games that ate important to you.

For the most part, no. Check out areweanticheatyet

Overcooked, Liars Bar, Ready or Not, Schedule 1, Elden Ring, Jackbox, etc . . . . . All work great as multiplayer titles on linux. There's a great trove of fun games that don't require kernel level anticheat because the the community of players isn't as toxic.