The modern automobile is safer, cleaner, more efficient, and more technologically advanced than anything that came before it. Yet those improvements have come at a cost. For many owners, mechanics, and independent repair shops, that cost is repairability.
A simple hardware modification is all you need there.
Find the antenna for the on-board modem.
Disconnect the cable that leads between that antenna and the car’s brain.
If necessary (if the car gives annoying/disabling errors after step #2), connect a high-ohm resistor between that antenna connector and the car’s ground.
After that, the car will forever think that it’s outside of signal range. And since operating while outside of cell service range is something even the most modern of cars still need to do, all of the car’s essential functions will still work. You’ll lose any internet connectivity features, of course. But in exchange, you’ll have completely and permanently disabled any possibility of remote telemetry.
Until you take the car in for servicing, at which point all that data will get downloaded to the service module and from there be transferred to the manufacturer.
Losing Internet connectivity features is a sacrifice many aren’t willing to make, unfortunately. Besides, this modification is a good way to void your warranty. And prob insurance too.