When booting Kubuntu 20.04.1 (LTS) iso the workaround of detaching /dev/loop0 device and then unmounting /isodevice was required, as in comment #27. Then setup finished.
When booting Kubuntu 20.04.1 (LTS) iso the workaround of detaching /dev/loop0 device and then unmounting /isodevice was required, as in comment #27. Then setup finished.