After a while of no updates to the actual ISO download of HoloISO, the creator of this SteamOS-like Linux distribution has announced the original is now dead. As it's being replaced by the newer immutable HoloISO.
The developer put up a PSA (public service announcement) on the original HoloISO GitHub page, and archived it so it will no longer see any updates at all and you cannot get support for it. They said the new immutable HoloISO is now "ready to be used as a daily-driving distribution".
What is an immutable operating system? Think like SteamOS and Fedora Silverblue. The idea is to give a read-only filesystem that gets replaced on updates. It's supposed to keep things more secure and stable, plus easier updates since it just replaces the main system.
HoloISO itself is designed to give you a close-enough version of SteamOS to use on other systems, and so the new immutable HoloISO should hopefully be more reliable. It's what AYANEO were going to put on the AYANEO NEXT LITE but they've since backtracked.
There's no current way to upgrade an existing HoloISO system to the new way it's run, but the developer mentioned they're currently figuring out the best approach to it. Update: 30/01/24 - version 1.1 now release supports migrating.