Indeed there are other things not working.
$ lxc launch ubuntu-minimal:bionic test Creating test Error: Failed instance creation: Create instance: Create instance: Invalid devices: Failed detecting root disk device: No root device could be found
I fear there is somethig seriously wrong. I will do a backup of all the containers using `lxc export. Would it then be possible to remove all lxd and zfs and reinstall again (so that the containers keep working incl. services like networking? If that would work, it would be perhaps a good point to get rid of blocked deleted images in zfs eating up my storage.