Secure Boot, TPM and anti-cheat

Secure Boot is a firmware feature that only lets signed software load during startup. A TPM (Trusted Platform Module) is a small security chip, or a firmware equivalent, that can store keys and attest to what software the machine booted with.

If a game can verify that the machine booted only trusted code, it is much harder for a cheat to hide in the boot process or in a driver loaded early. Some anti-cheat systems on Windows now require both features for certain games.

Most Linux distributions can boot with Secure Boot enabled, so the feature alone is not what excludes Linux. The harder problem for a vendor is proving that the whole running system is unmodified, since Linux users can legitimately change almost any part of their system. For this reason, requirements like these usually go along with the vendor not supporting Linux at all.

The Steam Deck is a special case. Valve controls its hardware and software, but a game's anti-cheat must still choose to work with SteamOS.