You picked an operating system, and we respect that choice. The EL variants do not, by default, configure virtual hosts in the way they’re done on Debian/Ubuntu.
Virtualmin supports either, but we don’t alter defaults provided by your OS packages unless we have a damned good reason. So, if you want to use it like Debian/Ubuntu, you’ll have to configure it that way. That involves adding a directive to the nginx.conf to include config files from the /etc/nginx/sites-enabled directory, and configuring Virtualmin to use that for virtual host configuration files.
To “migrate”, you can probably just disable the website and SSL website for the domains, change the configuration in Virtualmin to use separate config files, and then re-enable the website and SSL website feature after. Probably. I’ve never done it, as I use whatever the OS uses.