“Note that if you allow an autonomous car are Shabbos, you are probably allowing any use of computers or smartphones and even electric lights.”
Let’s stick to the point please. For what it’s worth, even if I had a truly autonomous car I would not use it on Shabbos in 2020 because of Maras Ayin.
But If you keep your cholent warm on a blech that you set up on Friday afternoon, then I don’t see why this kind of predetrmined use of energy is any more of a problem.
The premise is that the car is programmed to take someone on a predetermined trip at a preset time. Like a Shabbos Clock.
Or it could just follow a route from some homes to a shul or other Shabbos-appropriate place (NOT the Wawa) continuously through Friday afternoon to midnight, and again beginning Saturday morning. This is similar to a Shabbos elevator.
If you hold that either a Shabbos Clock or a Shabbos Elevator is Assur, then of course this convenience is not for you.