That’s not our module, but the person who brought it back to life a couple years ago (@RandomCamper) posted about it here: Vsftpd module revived
So, I tagged them, in hopes they’re around to answer questions.
It looks like that Perl module should be present in the Webmin module: https://github.com/rdmark/vsftpd-webmin/tree/2023-12-10/libvsftpdconfig
Maybe check your install to be sure the whole thing is there.