You don't have to lean on a special tool to know whether or not a Microsoft game will play properly on your Steam Deck. The Verge notes Microsoft has published a list of the Xbox Game Studios titles you can play on Valve's handheld, and it's mostly good news. Recent releases like Deathloop and Psychonauts 2 are listed as "Verified" (that is, known to play well), and you can expect 2017's Prey to thrive.
Forza Horizon 5 (and 4), Sea of Thieves, Fallout 4 and Quantum Break are some of the games labeled as "Playable." They should work, but you may need to spend extra time setting them up or dealing with quirks (such as using the on-screen keyboard).
You're out of luck if you want to play a few of Microsoft's best-known games, however. Gears 5, Halo: Master Chief Collection, Halo Infinite and Flight Simulator X are all deemed "unsupported" due to their anti-cheat tools.
This list only includes the games Microsoft offers on Steam. You'll have to install Windows (and lose official support from Valve) if you insist on playing the company's wider catalog. Microsoft said Steam Deck compatibility is up to individual studios, however, so don't be surprised if a previously unviable game becomes playable in the future.