The real trick is to never connect your TV to the internet under any circumstances. These things are displays, they don't need the internet to do their job. Leave that to the game consoles and streaming boxes.

I worry about the new cellular standards that support large scale iot.

Search for 5g miot or 5g massive iot or maybe even 5g redcap

Existing LTE is fine. If they wanted to embed modems in the TVs they could do it now. I'm guessing they simply don't have to, simply because a huge number of consumers will dutifully hand over their Wi-Fi passwords.

This is exactly the situation we're in with new automobiles...

While this is certainly possible, I’d imagine this sort of thing would be found quite quickly and would result in a massive lawsuit if not disclosed on the package.

It's going to happen on any device. It's a software thing. If LG isn't doing it, it's Netflix, Amazon Prime, etc. My PS5 basically shows ads on some system ui screens (granted mostly for "game" content but it still counts).