Back 4 Blood, the zombie shooter from Turtle Rock Studios has a fresh update out, and the developer has gotten it working on Linux and Steam Deck with Proton.
An important note though, is that this is "experimental" right now so there may be other issues. However, I've personally tested it on Steam Deck and it works quite well. You get a chat disconnection message often, and cut-scenes seem to stutter with the official Proton but other than that, it's quite playable and enjoyable on the defaults.
Here's what they said:
Developer Note: We have made an experimental change that we believe will make the game playable on Proton platforms such as the Steam Deck, SteamOS, and Linux. While this is not yet official support and has had limited testing, if you are a player interested in playing on these platforms, you should no longer be prevented from doing so and should join us on our Discord to discuss bugs specific to this platform.
What they've done is hook up Easy Anti-Cheat to work properly on Linux with Proton.
For a quick look at it on Steam Deck with default settings, have a look at my video below: