Update 25/01/23: Valve are now forcing the spoofing of a Steam Deck server-side, so the workaround is no longer needed.
In a case of what the heck? Square Enix and Luminous Productions just released Forspoken, which works on Steam Deck but it won't run on desktop Linux without spoofing it being a Steam Deck. One of those moments where I had to blink a good few times, wipe my glasses and let out a big sigh.
To run it on desktop Linux you can either load launch Steam directly with "-steamdeck" or by setting "SteamDeck=1 %command%" as a launch option for the game itself. No this isn't a joke. It's not entirely clear why but I'm not going to say the developer or publisher actively chose to block Linux desktop, it's more likely they just didn't think about what they were doing outside of letting it run on Steam Deck specifically (which runs SteamOS Linux).
Without that workaround, launching it on desktop Linux gives you this:
But when launching with the workaround, well it's a different story.
Doesn't exactly seem very stable either, it would completely crash if I picked a different overall graphics preset. Some individual graphics settings made it completely crash too. I also couldn't get it to go above 30FPS, with Vsync off and a limit set to 120FPS it just wanted to stay at 30FPS (and plenty below that).
Looks like a rough launch with it being Mixed on Steam so far and plenty of critic reviews have not been particularly kind on it either. At £64.99 it just doesn't seem worth the price.