This is the opposite of personalization. It's commodification. Instead of your car personalized to your specifications to fit into your niche, you get a dozen generic categories and decide that today you'll be summoning Generic Touring Vehicle but tomorrow it will be Generic Multi-Personnel Transport Vehicle or Generic Light Duty Towing Vehicle.
The fact that they offer fries in three different sizes doesn't mean yours is personalized because you picked the medium one.
Other examples of personalized things: A caricature of you drawn at a carnival, the local chef who knows just how you like your meal, that thing your nephew made you in shop class, etc.
In tech it usually means using the surveillance the company has conducted on you to make search suggestions and things like that. But people are increasingly finding that creepy and invasive, so it's not clear more of that is going to be a winner in the transportation market. Even historically it has been mostly backfill to rationalize the surveillance. Having some cloud surveillance technology literally following you around and recording your whereabouts isn't exactly the same kind of warm feeling you get from your favorite chef knowing how you like your dinner.
Whether those are frivolous, I think is in the eye of the beholder.
Robotaxis will be more personalized than privately owned ones. Rather than be limited to a single one-sided fits all form factor for all your transportation needs, you'll be able to call upon the optimal vehicle depending on whether you're commuting, hauling a load, going on a road trip, spending a lavish night on the town, or sending your kids to soccer practice.