I think you're talking about the really old version from the steam machines. The OS the Steam Deck uses (version 3.0+) is completely rebuilt and uses a different OS as a base (now using Arch instead of Debian)
The current, unavailable for general download, is Steam OS 3. Valve just refuses to put a number 3 anywhere, do they just pretend the other two do not exist.
BTW, there are a few "almost steam os" out there. I can vouch for Bazzite, it's fedora based and really good. Very welcoming for beginners, but had a lot of options of you want to dig a bit.
If you mean the old Debian based one, yes. SteamOS 3+ is arch based and released with the steam deck. Valve said they'd release a version for desktops, but have yet to follow through.