Good news for people wanting to play Remedy Entertainment's new game FBC: Firebreak, as it's releasing June 17th and it will be playable on Steam Deck (and so Desktop Linux too thanks to Valve's Proton).
I did email the developer to ask about if it will run, and if they planned any anti-cheat, which could have caused problems but they didn't reply. However, they did recently do a developer livestream where the confirmed very clearly how they're aiming for it to be Steam Deck Verified.
The Communications Director, Thomas Puha, was mentioning how it will run on lower-spec PCs. Then the Game Director, Mike Kayatta, jumps in to note "Steam Deck as well". After that the Community Manager, Julius Fondem, notes they're "aiming for Steam Deck Verified, that was very important for us".
Check it out at about 1:33:42

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FBC: Firebreak is Remedy Entertainment's first self-published game and will be available for $39.99 / €39.99 / £32.99.
More about it (from Steam):
FBC: Firebreak is a cooperative first-person shooter set within a mysterious federal agency under assault by otherworldly forces. As a years-long siege on the agency’s headquarters reaches its boiling point, only Firebreak— the Bureau’s most versatile unit—has the gear and the guts to plunge into the building’s strangest crises, restore order, contain the chaos, and fight to reclaim control.
Dive into the Federal Bureau of Control’s (FBC) unpredictable and extradimensional headquarters during its darkest—and strangest—hours. As one of the FBC’s fearless first responders, you and your team are on call to confront everything from reality-warping anomalies to otherworldly monsters... no matter the odds. Will you contain the chaos or finally lose control?
Remedy have said they will continue to expand it after release. In the press release they said "All future playable content, including new Jobs, will be free. Players will have the option to purchase cosmetics, but none of these items will affect gameplay, and there will be no limited-time rotations or daily log-ins".
You can also see the latest Hazards of the Job trailer from a few days ago below:

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