Theoretically finding how it transmits data and hitting it with a hammer

In most vehicles with onstar (Chevrolet mainly) you can pretty easily disconnect the cable that connects the computers to the antenna. You need to install a dummy load to keep it from turning on the check engine light but other than that it’s trivial. Once that’s done, the car will still collect data but it can’t send it anywhere. Just don’t take the car to the dealership for maintenance or they might “fix” the antenna connection for you

What happened to that slate car?

There was a quite a lot of buzz around it a few months ago

By banning cars for trains!

I'm curious about it too, especially knowing whether there are any car brands that are more privacy friendly than others.

Buy a used car without a cellular connection. I promise it's not going to explode.

Buy a motorcycle instead.