With a reverse proxy, I don't see how this would work. The whole way the reverse proxy works is you use a subdomain name ("jellyfin.yourdomain.org") to access Jellyfin, rather than some other service on your server. The reverse proxy sees the subdomain name that was used in the HTTP request, and routes the traffic based on that. Scanning only the IP address and port won't get attackers to Jellyfin; they need to know the subdomain name as well.