Ah... see, you two are about a decade too early for the OP issue.

I don't have a 2026-model car, since those cost as much as a house nowadays, but they also have a water pump; theirs with a microcontroller. Said pump won't work unless it's had it's special flavor of authentication handled so the computer in the pump (which adds non-negligible cost) can talk to the rest of the car. That's computer's only job is to tell the pump it's authentic and can work.

(I'm simplifying, I'm IT secops, not auto) Used to be there was a literal wire that ran from the turn signal stalk to the actual lightbulb. We replaced that with CAN bus, so the stalk just sends a "we're turning left" signal that the lights are listening for, like a home network where your computer sends a signal to the printer so you can print a document. In a home network, you might have a real threat vector of an attacker trying to intercept your locally-transmitted data, so there's a mild use case for encrypting everything to remove that risk.

In my car, there's no man-in-the-middle danger for someone trying to snoop on my turn-on-wipers signal. Other than aggregate data about how you drive, there's no data there to leak anyway, it's all operations. These manufacturers devised a system to 'protect' your car network, and are now leveraging it to spy on you (by harvesting your usage data in aggregate -- this guy likes to accelerate aggressively and turn without signaling) and also lock out third party parts by ensuring they can't talk over the local network because they are untrusted by the other parts.

There are documented cases where a car has been 'hacked', but those are generally... spoliers... cars with "genuine" parts with software vulnerabilities that don't need to exists in the first place, and maybe we could spend more time on ensuring the bluetooth stack can't even see the engine instead of ensuring the water pump must be able to prove it's legit.

(*Side note, While double checking my knowledge, I found this. It has a reference to MOST, and I can't imagine the self control needed to not name this 'Media Oriented Inter-Systems Transport' instead. I would not have made it.)

I think I'm preaching to the choir here, but back in early 2000s-2010s, we were still in a gilded age of car-can-have-computer-and-do-cool-thing, and now we are in car-must-have-computer-to-fuck-consumer. Same thing is happening in your phone, and soon will be happening in your house. "Sorry it's so hot in there, the non-samsung AC isn't compatible with your H0-US-3 model.