Possibly related, but I was able to download a distrobox image of SteamOS through BoxBuddy. Dunno if it’s legit or what, but I was able to play games through it (though made no sense to). This was a week or two ago that I saw it on the dropdown when installing a new box.
Edit: I see other people in this thread mentioning some old steamos so maybe it’s that I dunno, maybe I will check later.
Just opened it up to check… It is Arch. I was able to grab pacman and use it to get fastfetch to confirm (as if I needed to at that point lol).