Well, looks like the previous excitement around Back 4 Blood and the Open Beta for Linux users is over, as it appears whatever they tweaked recently now stops Linux players with Steam Play Proton.
As we reported recently, apart from a few issues it actually worked quite nicely. Sadly, this seems to be another example of Easy Anti-Cheat blocking Linux users from enjoying a game on their systems. Even though it's currently only a Beta, it means it's not looking good for the full release in October.
This is a continuing problem for Steam Play Proton, with the likes of Easy Anti-Cheat and BattlEye usually blocking Linux users. Right now then, it looks like we're back onto the waiting game for whenever Valve releases a build of Proton that works with them, which we know they're working on since they already announced it with the Steam Deck.
It is of course a reminder of what can happen without developer support in some way, regardless of it being a native Linux build or a Windows game run through Proton - unless the developer is testing, there will be times when they break. Less likely for single-player games but quite likely an issue for multi-player. We're hopeful the Steam Deck will really pull developers in for regular compatibility testing.