You are right about the typo - I have fixed it.
The mount unit is mnt-Disk.mount and your automount is mnt-Disk.automount
ONLY one can be started and enabled
If you want to only mount on access then disable the mount unit and enable the automount.
sudo systemctl disable --now mnt-Disk.mount
then enable the automount
sudo systemctl enable --now mnt-Disk.automount
It works this way - the automount unit activates the mount unit when you access the path - so you need both for this to work - and I assume you already have the mountpoint /mnt/Disk defined.