Just got my 512 GB Machine today. Its hostname is steamdeck and the default Linux user is deck. I would have expected them to at least change the hostname in SteamOS. No wonder all the Deck ready games use a Steam Deck profile if not even Valve bothered to rename the thing.
Wonder if it also sets the steamdeck environment variable.
I guess some of the games falsely seeing the Machine as a Deck check for Proton.