SteamOS version 1 'alchemist' and version 2 'brewmaster' have been
discontinued. No further updates are planned.

The SteamOS 'clockwerk' prototype has also been discontinued and will
not be released.

SteamOS version 3 'holo', as used on the Steam Deck, is a separate
codebase based on Arch Linux packages and does not use this apt
repository.