Valve developer Pierre-Loup Griffais noted in the Friends Per Second podcast:
On a console like Steam Machine, players have more reason to run online games with anti-cheat than on Steam Deck. So we are definitely working on this
Valve has included all Trusted Platform Module APIs so that developers can create their own anti-cheats.
Some solutions will be specific to SteamOS, and developers decide for themselves whether to make them compatible or not.
The company clarified that it helps developers as much as possible, but the timing depends on publishers and anti-cheat providers.