To my knowledge there really aren't any downsides to a diagnosis, as a matter of fact you may even have new legal protections under the Americans with Disabilities Act, or ADA: https://autismsociety.org/wp-content/uploads/2021/11/ADA-Fact-Sheet-1-1.pdf

You also have a right to not disclose your diagnosis per HIPAA, so long as you wouldn't need an accomodation.

I wouldn't even know where to get a diagnosis as an adult. All the resources in my area seem offer evaluations to children only.

I don't know about where you are, but here in australia, you don't need to take your driving test every year.

As for downsides, a dx precludes you from serving in the military, if that was what you were wanting to do.

A dx helped me a lot. I got answers for why i am the way i am. It also allowed me some room to move, in terms of allowing myself accomodations that other people don't need. Before i was dx'd i was really hard on myself. But now I've accepted that I am different and as such, i struggle with things that other people do not.

It should be noted i was diagnosed when i was 32, so quite late.

I felt the same a year ago when I realized I might share some traits described by autistic people. It was first a relief, a convenient explanation to most things I struggle with, and some “strange” traits of mine.

However, a diagnosis is very difficult to get in my country (years of waiting, not even sure I would get it one day). I decided not to do it because I don’t feel it would change anything beyond the validation. I don’t consider myself as truly autistic since I have no diagnosis, but I keep it in mind when I encounter difficulties, and it helped me a few times.