I think you mean explicitly open the port on your router, but even then that’s not true. Plex by default will proxy your traffic so that even closed off servers can be reached. It is pretty easy to disable remote access in the server settings though.
Error
Microsoft Pluton prevented an unauthorized file from opening. You are prohibited from opening this file because it may contain an unauthorized operating system.
File name: ubuntu-22.04.2-desktop-amd64.iso