Availability and location cannot be solved with a note pad.

Restricting the scope to those two problems would remove 1/3 use-cases and around half of the pages required (going by the "The Birth of a Product" section's bullet point list). It's an interesting exercise to think of the absolute simplest way to solve a given problem. As the author had been "itching to build an app for a while", I think solving the problem was not the only goal here - fair enough.

A shared AirTag could probably take care of the location issue easily. I assume that in this scenario with exclusively trusted users, trading off privacy for the convenience might be worthwhile.

One design requirement was that the car’s location is only known when it is available, which rules out AirTags.

And sure, relaxing that requirement would make for an easier implementation. But also worse acceptance by users.

Neither are needed to solve the problem of "splitting the gas bill".

If that were the only problem the author was solving, that would be relevant. But he is solving much more than that.

It's a personal app, a learning experience, and it was fun for OP to make it. I don't understand people's need to immediately react negatively to anything and everything they see. This isn't Adobe enshittifying their apps, it's just somebody who did a fun project, ffs.