Every current, major, third party AntiCheat system has supported Linux since 2022.

You are correct that they figure out a way to do it without kernel access when on Linux, and when the game devs take advantage of the support that they are already paying for, to help them customize/tweak the AC and the game to work together.

This is a fine solution, because 99.9% of cheats you can easily buy for money via a 60 second websearch only work on Windows, and there are many, effective ways to do AC that do not require Kernel Access.

Many AC systems do not need a TPM2 to work.

There were tons of AC systems that did their jobs before Microsoft pushed everyone to adopt TPM2.

As for as games running on Linux: Basically everything that is not using some cutting edge driver/feature from Nvidia works on Linux via Proton.

Thats the scenario that the major thirdparty ACs who have supported Linux since 2022 primarily target.

If a game or proprietary AC does not support Linux, that is either a deliberate business decision, or down to incompetence from the devs cough Facepunch cough.