Valve developer Pierre-Lou 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 it
Valve has included all Trusted Platform Module APIs so developers can create their own anti-cheats.
Some solutions will be specific to SteamOS, and it's up to developers to decide 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.