I don't remember how I did this years ago, but I suspect I made changes in config files on the command line instead of through Virtualmin.
So on a new server, at some point a self-signed certificate was used for ProFTPD. I've since added a proper certificate to Webmin/Virtualmin, but I can't see how I would make ProFTPD (through Virtualmin/Webmin) use it for FTPS connections. There are options in Virtualmin to copy the certificate to various other servers (Webmin, Usermin, Dovecot and Postfix), but not ProFTPD.
Is there a way to do this through Webmin/Virtualmin (other than, obviously, at Webmin -> Servers -> ProFTPD Server -> Edit Confg Files -> /etc/proftpd.conf) or must I do it via the command line?