Network not available then pushes to user login about steamos-ubuntu HOT 1 OPEN

@fr3f4ll not sure if you've sorted your issue or not but I've run into the same problem today.
Its a Ubuntu - Steam issue not a Steam OS issue.
I am assuming you are getting:

Fatal Error: STEAM needs to be online to update. Please confirm your network connection and try again

If so, for everyone else who is having this problem, the fix is documented on the bottom of the blog post here - https://linuxhint.com/install_steam_games_ubuntu_1804/

To then make this work on SteamOS (as its running under user Steam, you will need to:

1. Login with the Steam user (if you don't know the password change it first)
2. create mkdir ~/.steam/ubuntu12_32/steam-runtime
3. open terminal and type steam this should start steam and do its preflight checks.
4. reboot your machine and Steam OS should start

from steamos-ubuntu.