Comment by nusl

Many games do that, yes, though with varying degrees of success and often they get beaten by cheat tools. That's not to say that kernel-level anticheat can't get beaten, though there is a reason why games like Valorant have fewer such incidents. The cost/effort required to bypass the anticheat is way higher than some client-side checks.

Some games do choose to go the route of server-side authority, only showing what the client should be able to see, though I understand that's super compute heavy. Final Fantasy XIV does something akin to this, but players still develop client-side plugins to make their lives easier (higher-than-allowed camera zoom-out, displaying hidden boss mechanics when the client receives them, etc)

Cheats are also financially supported, specially in higher-profile games like Fortnite, Valorant, League of Legends, or similar, so the incentive to produce higher quality cheats exists.

People have been caught by pretending to play but actually screensharing the view of a pro player on their account, so I suppose that won't cover this :P