This is going to sound really weird, but... can reading be considered a distraction or a stim? I know usually having AHDH makes it hard to concentrate for long, but I was always reading in class as a child and my doctor thinks I could be an exception because reading could have been my constant escape from reality.
That sounds like what happened to me when I was younger. I totally hyperfocused on reading! I was always reading, no matter what. In class, walking down the hallway at school, in my room at home, walking around the house… not at the dinner table because we weren’t allowed.
That got harder in university, but I still get lost in books when I manage to start reading something.
Other things can be harder to focus on, but reading? Man, words are my life.