It’s not restricted to Plex. The TV’s “root certificate” , which is installed by Samsung, is expired.
The solution for you – Add the exception in "Settings - Server - Network - Show Advanced - IP addresses allowed without Auth.
Make certain there are no leading or trailing spaces (Plex/web doesn’t parse them out for you)
Before you ask further, Asking Plex to support a device which isn’t supported by its manufacturer anymore – There’s nothing we can do. We don’t have the ability to update the TV’s firmware.
This is planned obsolescence – or – just plain laziness on Samsung’s part
