Would be cool for a "console box".

There's a few forks of SteamOS that do the job at least.

Well SteamOS is Arch based but running a LTS kernel with backported changes in a ummutable way with everything sandboxed in Flatpak so it's quite unique but idk why anyone would want to run it on their desktop, if the immutable aspect is so interesting ro you you can try Fedora Silverblue, Vanilla OS and co. but none of those is in a state that I would recommend as "just works" for a desktop experience, if that's the majore goal Debian or Fedora with Gnome are probably your best options.