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.
The problem with putting it behind a VPN is then all your users have to be on VPN.
Self-service IP whitelisting would be easy and let all clients work without trying to hack in a separate VPN client.
The only thing that would suck would be if you were on a mobile link while moving and swapping towers your IP would change so you constantly get kicked off.
But if you were so inclined you could VPN to your own house and your IP would stay the same.