The latest plea for official Proton support started on Reddit, where Scout339v2 shared their screenshot of Rust running "on a server with EAC disabled to show that the game already works perfectly on Linux." Disabling Easy Anti-Cheat (EAC) is the key factor here, and part of a broader conversation where Facepunch and its Linux/Proton userbase don't see eye-to-eye.
While it's true Rust runs on Proton, you can't join official servers, and most unofficial servers, with EAC disabled. Facepunch considered changing its stance in 2022 when the Steam Deck launched, but didn't end up introducing official Proton support. COO Alistair McFarlane said at the time that Linux is "safer for cheat developers," and that trying to support EAC on another platform could reduce the team's ability to support Windows.