https://wccftech.com/microsoft-xbox-steam-deck-compatibility-list-no-halo-gears-flight-sim/

With Valve’s Steam Deck now out in the wild, Microsoft has clarified which of their Steam games will be compatible with the new portable gaming PC, and it’s missing some pretty major titles. While some notable games like Deathloop, Psychonauts 2, Sea of Thieves, and Forza Horizon 5 are supported, you won’t be able to play any Halo games, Gears 5, or Microsoft Flight Simulator X on Steam Deck. According to Microsoft these games won’t be supported “due to anti-cheat.”

Here’s the full list of Verified, playable, and unsupported Microsoft Game Studios titles: