There currently is no supported way of doing this, since it might lead to catastrophic data loss.

If you are sure you know what you're doing, you're already on the right track:

1. Nummerierter ListenpunktMake sure there is absolutely no important data in the sectors of the disk you're going the remove (starting from the end of the disk)
2. (Make a backup before proceeding to be really sure)
3. Shut down the VM
4. Tell ZFS to shrink the disk (e.g. zfs set volsize=XXXG rpool/data/vm-<vmid>-disk-0, use zfs list to find the correct one)
5. Run qm rescan <vmid>
6. Start the VM to verify

systemctl disable --now systemd-timesyncd.service
systemctl enable --now chrony.service