Issue

[email protected]:~# unattended-upgrades --dry-run
Traceback (most recent call last):
  File "/usr/bin/unattended-upgrades", line 1998, in <module>
    sys.exit(main(options))
  File "/usr/bin/unattended-upgrades", line 1714, in main
    if conffile_prompt(item.destfile):
  File "/usr/bin/unattended-upgrades", line 929, in conffile_prompt
    with open(prefix + conf_file, 'rb') as fp:
IsADirectoryError: [Errno 21] Is a directory: '/etc/qemu/fsfreeze-hook'

Solution

apt install --only-upgrade qemu-guest-agent

Cause

https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1820291