would you please share the import command ? is something like "zpool import" ?ZFS panic on pve root after power outage ... that comes not unexpected. If you cannot import pool on any live-linux boot you need a new pve installation.
if "zpool import" says nothing to import ?What about "zpool import -o readonly=on rpool rpool2 -f -d /dev/disk/by-id" from your live-ubuntu ?
When you are using zfs you need to learn troubleshooting and to test how to restore a full system.
Operating a ZFS without UPS with server control is even negligent as you see yourself.