Adding onto the other comments, if you have admin access to your network router/firewall you can configure the incoming port forward itself to only allow specific IP addresses while dropping traffic from any other internet WAN IPs. It’s a bit like using the Jellyfin whitelist/blacklist but doing it at the network level. This drops all unwanted internet traffic to that port at the firewall before ever reaching the Jellyfin software. Downside is having to occasionally update the firewall whenever there are IP address changes.

This is probably only feasible if you only have some specific Jellyfin clients in mind to accept connections from, not any random person from any random WAN IP address.