First of all, open the TV and disconnect the wireless radio from the main board, on mine (Samsung) it was just unplugging one cable (AI or Google it). I dislike doing stuff like that, but it was easy in my case, maybe you'll be lucky, too.
Second, never use the "apps" built into the TV.
Next, don't plug Ethernet into the TV. Plug HDMI cables into the TV.
Use a box of your choice on the other end of the HDMI cables. This is now the box that you trust. (Roku? Shield? Blu-ray? MacBook? PC? Linux? Playstation? XBox? Whatever you want.)
The Smart TV itself is now fine. Choose the devices you plug into it to play content. The TV just shows it.
The thing I'd be worried about when doing this is spending $1000+ on a TV, then realizing it has some sort of pre-downloaded ads that it shows on the main screen ("sign up for your free six months of HBO Max!") or otherwise has a nag prompt that appears to tell you to connect to WiFi. I think that would be basically intolerable.
> First of all, open the TV and disconnect the wireless radio from the main board
This. Never trust software switches. See my other reply for what I suggest instead of "streaming boxes" that aren't any better than the TV firmware.
While practical advice its just odd to me there's no major legislation or movement or activism or boycotts about this. We just accept our TV might be silently recording everything we say in our home and the fix is to not plug it into the internet.
> disconnect the wireless radio from the main board
Why?
> Use a box of your choice on the other end of the HDMI cables. This is now the box that you trust. (Roku? Shield? Blu-ray? MacBook? PC? Linux? Playstation? XBox? Whatever you want.)
If they choose a Firestick or Roku what's the difference? XD
> disconnect the wireless radio from the main board
Can you explain why you can't just not give the TV your Wi-Fi password?
Or are we worried about the case when the TV did have Wi-Fi (due to it being mandatory for some initial setup, say), but we don't trust that "Forget Network" and "Wi-Fi off" are actually honored?
Suppose the device surreptitiously reconnects to Wi-Fi in spite of being told to forget it. You may be able to block it in your router and failing that, change the access point password.
No?