Ubisoft suggest posting on their forum for Proton support in Rainbow Six Siege
Now that getting games that use BattlEye for anti-cheat working on Linux (either native or through Proton) is easier, an Ubisoft rep suggests people post in their forum to show demand for it.
How to setup OpenMW for modern Morrowind on Linux / SteamOS and Steam Deck
How to install Hollow Knight: Silksong mods on Linux, SteamOS and Steam Deck