Recently there was a thing where VAC would erroneously flag AMD’s antilag+ feature as cheating, and issue a ban.
AMD then quickly disabled the feature by default but now Valve also patched detection for it and is now, at least according to these patch notes, reversing the bans.
Depends on the game iirc. If you get banned in a Valve game, you don’t get to play multiplayer in any Valve game.