Bad news: your car is a spy. Every major car brand failed a recent privacy and security test from Mozilla. You’re probably driving around in a "privacy nightmare" that may collect information as sensitive as your race, health status, and sexual activity.
Pretty sure you can disable OnStar. Sirius should be receive only but I’m not certain.
Depending on the apps you have on your phone you may already be leaking lots of info.
I go through an app refresh every so often and remove those that I haven’t touched in months. Even that only gets me so far, I’m sure.