Yep - this. I absolutely abhor "smart" TVs for just this reason.
But, even lack of internet sometimes isn't enough. I recently, and inadvertently, left the wireless adapter on my TV enabled, after having to temporarily join it to my wireless for a firmware update (digital TV tuning needed updating for my region). After I was done, I cleared the wireless config, but I didn't think to go into the other menu where you can entirely disable the wireless adapter.
Little did I realise that meant the TV started broadcasting its own SSID, for friggin' Apple Airplay or some other shit. I found this out when my 9yo daughter was suddenly exposed to some adult content for about 10 seconds. Best guess is a nearby neighbour mistook my TV for theirs.
I've obviously disabled the wireless adapter again, but this has been a terribly difficult lesson I've had to learn.
For anyone concerned, my daughter is OK. My wife had a good chat with her about it. She had considerably more talking down to do with me - I was ready to start knocking on doors, to have my own chat.
How well does Plex run on a RasPi (or other SBC), and have you found a good remote control solution for it? I'm still using Plex on Google Chromcest TVs - the li'l remote just makes it so much easier.