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.
Still gives a good idea of the proportions though and I’m willing to bet that most of the Steam games missing are shovelwares that no one ever installed.
https://www.forbes.com/sites/erikkain/2014/04/17/nearly-37-of-all-registered-steam-games-have-never-been-played/?sh=699792182146