http://freenas/ui/vm
Step 1:
Virtual Machines > ADD > Linux > Name: PiHole > Next
Step 2:
2 CPU's and 2 GiB
Step 3:
Zvol Location: raid/VirtualMachines Size: 60 GiB
Step 4:
Next
Step 5:
Upload an installer image file: /mnt/raid/VirtualMachines ubuntu-20.04-live-server-amd64.iso
Step 6:
Next Submit
Boot VM
Update Ubuntu
sudo apt update && sudo apt upgrade -y sudo apt autoremove
Install Pi-hole
curl -sSL https://install.pi-hole.net | bash
Update Pi-hole
pihole -up
Upgrade Ubuntu
do-release-upgrade