>> 2) My car. Even though it can update over wifi, and by other means, it never tries to do it unbidden.

Today. That could change tomorrow. We already have forced updates for popular operating systems. Mandatory "safety" updates for car software will come one day.

I'm waiting for the day that different states implement different software rules. Imagine if Nevada implemented speed-governors but Texas didn't. I see a world where everyone has to pull over at the state line to allow their car to reconfigure software in order to accommodate local rules.

My Eero wifi defaults to 4am for updates, which is changeable, and it warns me with a push notification the day before. I appreciate whoever implemented that particular subsystem.

You probably turn your TV and Nest on less than once per year. It's much easier for always on devices to update when they're not in use than an item like a scooter, which when it's off, it's actually off.

That said, I don't know why you would ever connect a transportation device to the internet. All of my vehicles are too old to connect to the internet, but when I finally have to replace them, the first thing I'll do is physically remove the Wi-Fi/cellular antenna

You can just do the equivalent of a blue-green deployment: you have two copies of the firmware, a flag that tells you which is active, and a tiny bootloader that respects that flag on startup. At any point during regular operation the firmware can update the other copy, and once done toggle the flag. Next time the scooter is started it uses the new version. If the device is shut down during update it continues to boot from the old version, and just tries again next time. Bonus points if you have a small watchdog that toggles the flag if the current version fails to boot.

One pretty understandable reason for a transportation device to update itself is for new GPS ephemeris data. I think it would be cool if there was a device protocol that somehow securely promulgated such data from devices that are expected to be well-connected, like your smartphone, to "things" that are not, like watches and cameras and scooters.

how do car auto updates work?

I would inclined to believe that maybe the manufacturer sends out an email or sms to notify you of am update and then you choose the time, while also being given a change log of what exactly is being updated.

otherwise what would prevent a bogus server asking for an update you have no idea about and installing something malicious and - whoopsie daisy - your car grows legs and disappears?

Yes, I have a proper car from a real car company. They shipped working software the first time and "updates" are actually recalls for which the owner is notified, at the time of annual service for minor issues, or by mail for major issues.