Some TVs will present a popover warning that they have not been able to check for updates for a while, after being disconnected for some time, and you can't close that without letting them connect (even if you are just using the screen to display content from an HDMI slot rather than using any of the other TV features).

Not sufficient, given reports of TVs and other devices automatically creating mesh networks. Your disconnected TV could talk to your neighbour's connected one. If anything, I wonder why LG isn't already doing it.

Edit: Getting pushback asking for evidence (fair). Most recently I read it in an HN thread a few years back. I thought it was a TCL TV, but I can't find it anymore. It wasn't Samsung's WiFi Direct, which I don't think was ever on by default.

Lacking better evidence, I'll admit I'm probably wrong and no TV has been documented doing this (yet).

“or similar” like what?

Streaming sticks suffer from the exact same problem.

The Apple TV is the only device I know of in this space whose business model is not selling your data to the highest bidder.

I have connected it to my network and then blocked it off the internet via Pi-hole. That way, I hope, it'll not try to scan for other open networks.

Part of the issue is many TV's these days are essentially bricked until you connect them to the internet to "activate".

Just disable wifi. Occasionally factory reset, hook up to wifi for firmware update, then disable again.

All smart TVs should not come with WiFi or Ethernet controllers.