“Every build of a Steam Deck image can be found at https://steamdeck-images.steamos.cloud/steamdeck/"
SteamOS updates by writing a new read-only Btrfs root to an inactive partition and switching over. iliana repacks Valve’s image, adds a kernel package, randomizes the filesystem UUID, and serves the result to steamos-atomupd. The build ID must look like YYYYMMDD.N or the updater refuses. Valve ships the atomic updater and leaves the documentation to strangers with root.