It is! A new version, in fact. It includes Proton. (I'm not sure if SteamOS v2 and below were already Arch-based, but it's interesting to know that v3 is, give

It is! A new version, in fact. It includes Proton. (I'm not sure if SteamOS v2 and below were already Arch-based, but it's interesting to know that v3 is, given that the Steam Linux Runtime is mostly Ubuntu-tested)