Today, just don't connect your smart TV to a network, and you should be fine. (Assuming there's no open/passwordless WiFi networks nearby.)
If/when devices start shipping with cellular modems and eSIMs... honestly not sure. Faraday cage? Physically remove the modem? (If that doesn't prevent the device from booting.)
If/when devices start shipping with cellular modems and eSIMs... honestly not sure. Faraday cage? Physically remove the modem? (If that doesn't prevent the device from booting.)