[… I deleted the reverse proxy and the virtual hosts I created but now when I ping jellyfin.mydomain.com I get the address of my nethserver. …]
I think you shoud check if it is present, and remove it, jellyfin.mydomain.com under system->dashboard → hostname/alias.
because when you setup a new LE cert for, nethserver automatically creates a new alias with that FQDN. (hope it’s true I’m relying on my memory)
Check my post about a similar argument here: How I expose services both to Internet and to LAN - SSL enabled
hope it’ll be usefull to you.
bye