Hello,
You could simply call the external script which executes:
virtualmin modify-all-ips --default-old-ip --detect-new-ip
… in Addresses and Networking ⇾ Dynamic IP Update page by setting Dynamic DNS service option to Run external script …
Please give it a try and let me know if that works for you.
Also, I would suggest spending a few extra bucks to get a static IP. I personally have been doing it for the past decade, and it was never more than $5/month. I think this would be a better approach, if you want your home server to be always available.