It's trivial, and many hacks for windows required loading unsigned drivers (functionally equivalent to kernel modding)

However, it's a bit of a red herring. People also do bootloader and virtualization hacks, some also mod the bios or do spychip hacking (often called negative rings, effectively privilege rings lower than zero, but that aren't actually modelled as privilege levels within the cpu)

However however, that's also a bit moot, because DMA hacking exists. You don't even need to load the hack into the target computer; you could read and write system memory directly from another device entirely.

Plus there are other non-invasive cheats, like fake hardware mice with vision-based aimbot.

This is all just a smokescreen and security theater. Partly trying to 'raise the bar' to stop cheap/low effort cheating, but also just as an excuse. This is for corporate and shareholders, not developers.

The only real solution to cheating is heuristic analysis, peer detection and attestation, and letting players block interactions with people they think are cheating

Client-side anticheat only exists to spy on you and make marketing departments feel nice.