In fact, they have made a sleek step-by-step guide on how to do it:
https://store.steampowered.com/steamos/buildyourown
If you don't like being dependent on a distro which more or less is in full control of Valve you could also try Bazzite, which includes a ton of nice to have extra features aswell:
SteamFork - https://github.com/steamfork
ChimeraOS - https://chimeraos.org/
Take your pick.
My point is that you have all kinds of choices (including Bazzite and a earlier version of SteamOS) to run Steam in a couch/console setup RIGHT NOW.
I’d really like a way to have my PC in one room and use it on any TV. I know Steam Link exists but it’s a bit clunky.