Thank you, gpatel-fr! I will attempt everything this evening (in about 12 hours or so).
One last question: notwithstanding the systemd-resolved / NetworkManager aspect of the equation, would the above instruction cause all DNS inquiries made TO the host (i.e. the router will be directing DNS inquiries to the host IP) to be forwarded on to the LXD container that will be running the DNS resolver (PiHole)?