Disclaimer: I haven't tried any of this myself, I've just been looking into it as I am/was considering buying an LG TV.
If internet is really required, I'd personally flood such an LG tv with fake data - add a raspberry pi to provide it with looped audio streams for the microphone, fake bluetooth devices, and so on. But it's still probably a drop in a bucket.
I'd just open the TV and yank or desolder the mic out. Or use the TV as a dumb monitor -- don't connect it to WiFi or Ethernet. And use an external Kodi/AppleTV/whatever-rocks-your-viewing-boat
This is not sufficient (for some of these devices) - they will automatically connect to an unsecured hotspot.