While it's supposed to be relatively easy for games with anti-cheat like BattlEye and Easy Anti-Cheat to get working on Linux and Steam Deck, some developers are having issues like Fatshark with Warhammer: Vermintide 2.
This particular game uses Easy Anti-Cheat, which is supposed to be a case of ticking a few boxes and making sure things are in the right place to allow EAC to work with Steam Play Proton but it turns out it might not be that simple for every game. A shame, but not a big surprise, as if it was truly that simple for every game more would have done it by now, and considering how big game projects and code are, there's likely plenty of smaller gotchas developers need to deal with.
A rep from Fatshark posted on the Steam forum to give an update on the work to get Warhammer: Vermintide 2 playable and it's not good news. Despite chatting to Epic and Valve, they couldn't figure it out and now their team is working on the upcoming Warhammer 40,000: Darktide.
Here's what they said:
So we have performed all the requisite steps to have this work. We've ticked the boxes in the EAC portal, included the files in the appropriate places. Problem is, as you can see, it doesn't work in this scenario. We've been in touch with both third parties (in this case Epic and Valve), but we're at a bit of a roadblock truth be told. Those who would work on really digging in to the weeds on this are indeed digging in to Darktide weeds, so aren't able to spend sufficient time liaising with Valve and Epic to figure out what's causing the 'simple steps' to not be as simple as they sounded.
In short, work on this is on hold for now. We'll bark up this thread should things spin up again.