I suggest fingerprint readers that enable & encrypt this level of data owner by owner.
No live finger print - no apps.
There would be a service / valet key as required - but apps / settings would only be enabled by the fingerprint reader. Perhaps the ignition key does what it does now, and the fingerprint does the rest.
The reader scans several fingers for each driver as part of the setup in case of chopping board injuries, and scans for a pulse to make sure someone hasn't done something gruesome.
Those who want to avoid apps on their car entirely, seeing apps as truly the work of the devil, only use the service key and never the fingerprint reader. This turns the object into a car again.
The majority, who will want apps, use the fingerprint reader.
Something will need to evolve because once the driver has bags of time because the car drives, they will want connections / apps to do work / leisure in the car. Those who only use the valet key will install a library shelf for books to read during traffic jams.
When you sell the car & key you can wipe your settings / fingerprint entirely (perhaps with combined use of the service key and your fingerprints) or trust that the encryption level will be good enough to keep hackers out. Those with a different mind-set will not think about it anyway and still get the same result.
By the time the iPhone 100 can hack the encryption level of your one-time car, you should have changed passwords anyway, or indeed be dead and not caring as much.