gamemoderun mangohud %command%
I've played it a ton with my friends and I've never really had any issues with it. Runs extremely well and the devs support it well.

Only issue is that the cursor in game shows up black. Annoying, but no loss in functionality.
mangohud gamemoderun PROTON_ENABLE_NVAPI=1 %command%


When I change the settings in the "options" menu, the game freezes/becomes unresponsive. After restarting the game, the setting seem to be saved. Playing "Borderless Window" works fine.
Game started without tinkering, too , but videos were black screens and the intro could not be skipped. I must switch to 6.21-GE to see the intro video (instead of black screen) and that works fine.

gamemoderun %command%

No problems so far ! Been playing it for about an hour with 0 issues , runs great and I even turned the graphics settings up to "dream". Using a controller is a little annoying on the menu for selecting your classes , but that has little to do with steam or proton.

gamemoderun mangohud %command%
Game has bugs, but not related to Linux

Works just like windows
The Closed beta is full of bugs though but those were also reported on windows so it's the game's fault.
Limited to 30FPS
Lots of text and interface elements are very small. There's currently no option to increase UI scale.
The game is still in beta, so hopefully there will be improvements before the final release. It's definitely playable, but there's currently no built-in controller support, so all the interactions are done via mouse and keyboard emulation. This wouldn't be so bad if not for the lack of UI scaling options, which both makes a lot of the text hard to read, and means that some of the buttons you have to click on are really small on the Steam Deck screen.
With a bit of UI polish and native controller support, though, this could be a great Steam Deck game.
Going to a from a workspace or alt-tabbing in or out can cause it to hang and will take seconds/minutes to fix itself