They have kernel access... They can control anything since they're in the kernel. And yes, I've seen it.

If you remember back in the late 2000's early 2010's there were a boatload of apps that would hook into games to do things like display overlays for chats (Teamspeak for example, overwolf as another.) some kernel anti-cheats would stop those processes from starting up.

But don't take my word for it.

https://www.pcgamer.com/according-to-experts-on-kernel-level-anticheat-two-things-are-abundantly-clear-1-its-not-perfect-and-2-its-not-going-anywhere/

I'm less worried about developers abusing kernel access, and more concerned with potential vulnerabilities introduced for third-party actors to exploit. Rigney cited two examples: the infamous Extended Copy Protection (XCP) from Sony, which bad actors used to compromise affected systems, as well as a backdoor vulnerability introduced by Street Fighter 5's kernel level anticheat. In 2022, a ransomware developer also took advantage of Genshin Impact's kernel level anticheat to disable antivirus processes.

Introduces backdoors to be used by malicious actors.

https://www.pcgamer.com/the-controversy-over-riots-vanguard-anti-cheat-software-explained/

Vanguard detects software with vulnerabilities which could be exploited by cheat makers, and blocks some of it.

Blocks external softwares that it deems "vulnerable"

https://old.reddit.com/r/gaming/comments/xf1cwr/the_insanity_of_eas_anticheat_system_by_a_kernel/

This is far from the first time that boot level firmware or kernel mode code inserted via patches or drivers have been used to install spyware, but every time I see it happen I want to warn users about the consequences, and provide some information about the danger.

Kernel devs beg users to not allow this shit.

Just look it up. All sorts of articles and experts have spoken on it.