I tried testing a movie from my home server in plex through firefox and repeatedly got this message, even after reloading.
I knew that they had paywalled the apps on mobile and streaming from outside the network but now they have also blocked watching your own movies through your own hardware.
I do get the point that making software should be able to sustain people but I dont see the move of plex as a fair thing to do. Yes, they have made great software but taking your home server hostage feels like the wrong move.
Even a pop up that says "we need you to donate please" would have been fine. make it pop up before every movie, play donation ads before any movie but straight up disabling the app is kinda cruel.
Anyway, i have switched to jellyfin and it is insanely good. please give it a try. you can run it alongside plex with not issues (at least i had none) and compare the two.
In any case, good luck. Let me know if you need help.
I can't speak for OP, but I self host lots of stuff, have literally dozens of services running, have an Ansible repo to manage it all and routi some stuff through a VPS, not to mention my day job has included managing services in one way or another for a long while. This is to say, I know what I'm doing. I couldn't setup Plex to work the way I wanted to, they expect it to run in a docker with network set to host mode, I couldn't find any way to tell Plex that my living room TV was in the same network, it just wouldn't accept any connections as local. I know I shot myself in the foot here by not letting it run with network on host mode, but I shouldn't have to, the port was exposed, I could reach it through the local network IP, but I wasn't able to stream any content locally.