Just saw this…CentOS Stream is not supported by Virtualmin at this time, and may never be.
It’ll probably mostly work if you install CentOS 8 and then convert to Stream, but you’ll diverge from the supported OS over time, and it will eventually break, if Virtualmin doesn’t have some kind of support at that time. I don’t know what that support looks like, or if we’ll ever have resources to implement it, though. So, I strongly recommend you not use CentOS Stream with Virtualmin in production at this time (and maybe never).
CentOS 8 is fine. You can convert to Alma or Rocky at any point, and they will be fully supported by Virtualmin and installer quite soon.