> the therapist said that she had rarely been more certain of a positive ADHD diagnosis
> my utter failure as a student, the huge highs and lows of my professional career, my distrust and lack of respect for authority of any kind, and my pride in my achievements as an autodidact
Oh yeah. I'm with you.
People's experiences inside their head are amazingly different, but society treats them the same. Some have inner monologues, some don't. Some have aphantasia. Some have prosopagnosia. Some are left handed, which was once considered evil ("left" is "sinister" in Latin, from another autodidact).
We used to label people as one of: normal, genius, retarded. We are becoming more nuanced now and exploring "neurodivergence". The label you have been given is ADHD. One day it will be much more nuanced.
Embrace it. It's not negative, it's society recognizing you and me and our type.