I had a debian stretch 9.x with webmin 1.920 ... I updated/upgraded to Debian Buster 10.x. My webmin 1.920 is still running fine.
as it is said: Never run the install.sh script to upgrade or renew or to try to repair an existing Virtualmin system!
i wonder how to update/upgrade to 5.0 version on my freshly updated buster as it is not "Start with a freshly installed system"