GDPR has a weird quirk of applying to all EU citizens whether or not they’re currently in the EU. Cars are physical things and it is harder to make different models. A check of “Is California billing address? Show button. No? Don’t show button.” would be trivial to implement and would probably result in enough money to make it worth it.
That part is currently illegal even in the US. So, baking it into an app would be a bad idea. Most of the time companies do illegal things, they try to be less explicit.