Just never connect it to the internet, or (even better) set up a PiHole and block the TV’s telemetry requests. I say the PiHole is better because then you still get all of the benefits of a smart TV (like native streaming apps) without all of the horribly invasive data mining.
If you want the benefits of a smart TV without connecting it to the internet, then maybe a connected PC would be a better solution. Something like an Nvidia shield connected to the TV, while the TV remains offline. That way you can maintain control over the computer, instead of trying to control what the TV collects and sends.