Riot's Valorant rootkit is active from boot and actively monitors everything you run and will block things it doesn't like or doesn't recognize.
Most of the other kernel anticheat rootkits are more polite and don't run until a game starts them, at least.
In general having a bunch of random stuff from video games running with kernel permissions is spooky. You never know whether someone will find an exploit in one of them, or if it will cause performance, stability or data integrity problems.