Depends on the ISP. Many don’t allow you to use one they didn’t provide.

You don’t have to rebuild the proxmox hosts to remove the cluster. I made the same mistake last year sometime and was able to remove the cluster and each of the proxmox machines works as it should standalone. I don’t recall the exact steps but it was very easy. A quick search for “proxmox remove cluster” gave me this result and from what I recall these are the steps I followed as well. https://rostislavjadavan.com/posts/promox-delete-cluster

Brilliant! Thank you.

I love the window opening and closing animation, like a CRT TV being turned off. How is that achieved?