This is useful for running Plex over port 443(HTTPS), it's important to go to your Plex server settings and change the following settings.
Remote Access - Manually specify public port = 443
Network - Custom server access URLs = https://plex.EXAMPLE.COM:443
It's also recommened to use a firewall such as ufw to deny port 32400 externally as Plex still pings it and sometimes uses it dispite having set 443.
Doing this also allows you to run CloudFlare in front of your Plex server which can improve peering.