The best place to see this information is to look at the CHANGELOG file that is part of the Virtualmin and Cloudmin packages. You can see this at /usr/libexec/webmin/virtual-server/CHANGELOG or /usr/libexec/webmin/server-manager/CHANGELOG . Or on Debian/Ubuntu, the path is under /usr/share instead of /usr/libexec.
Any chance you would consider making the changelog visible from webmin/cloudmin? It would really be a nice feature to be able to review this information without having to drop in to the command line. I hope you consider it, as I think it’s important to see the changelog at all times.