I am not really interested in an immutable desktop OS but that incus OS sounds interesting. I use Proxmox and if prox were to be immutable I wouldn't mind that.

I totally agree with the idea of replacing Proxmox with something more immutable.

IncusOS seems like a strong contender.

I've also considered installing Proxmox with ZFS Boot Menu to get a rollback capability. I'd need to figure out how to properly manage state when multiple storage providers are in use. Like for example, what would happen if the pool for VMs had newer data than the root snapshot I roll back to? Even with the answer, obviously the overall theme is Proxmox is not designed to operate this way.