Thanks for the intro to NixOS. I was trying to remember one I had seen & forgotten and I think this may have been it.
I have been playing more and more with UTM in the Mac world and it's encouraging how mature it seems already and hopefully can be picked up into NixOS, Sandstorm, etc.
I like proxmox more personally, however have changed my stance recently where nix and sandstorm could just be run in a proxmox vm and then provide more of an IaaS role. The newer versions of ProxMox are even easier and they were pretty OK the past 5-7 years.