its not hard to do measured boot with attestation and a set of trusted kernels. if you can check the kernel signature and config you know if the type of security anti cheat needs is there (memory isolation, lockdown, no unsigned modules). valve can set up a universal signing key list with steamos, ubuntu, cachyos, plain arch and all the other big distros. a lot of games already need a tpm on windows so hardware compat is not a big deal.

the problem is anti cheat vendors see linux as a small market so its not worth the effort to make it work. maybe valve can help by giving display priority to games that support linux and a warning banner for those that dont. or team up with epic games but gaben would probably have to invite tim sweeney to valve hq and personally explain it all.