The following error, updating dom0 :
- tar: /var/lib/qubes/dom0-updates: Cannot open: No such file or directory
tar: Error is not recoverable: exiting now
Dom0 updates dir does not exists: /var/lib/qubes/dom0-updates
Seems to be fixed with the following commands in the template used by your updateVM (my case whonix-gw, which is gateway for sys-whonix updateVM:
sudo mkdir /var/lib/qubes/dom0-updates sudo chown user:user /var/lib/qubes/dom0-updates
Restarting the updateVM is needed for the VM to reload with the correct setup.
Reference: https://github.com/QubesOS/qubes-issues/issues/3620