I think "just fine" would imply you can invoke hyperfocus whenever you want. In my experience, it happens with the most undesirable things at the most undesirable moments.

But I know so much about randomly WW2 battle and military boats and airplanes that was critical to know at 3am when I had a full docket of stuff to do the next day...

I can relate. Also, sometimes I can even invoke it on things I want to. However, I just can't turn it off when needed.

I think that’s true. If I want to focus on the thing that is my current obsession I can invoke that focus whenever I want. Never mind if I’m at work, in the shower, or at a birthday party. It’s just not very useful to achieve the goals you probably have at those places.

That seems to contradict my third sentence. Hyperfocusing does not mean choosing what to focus on. My point was, ADHD to me is not an issue in focusing. It's an issue with choosing what to focus on.

Understood, thanks for clarifying. In my case, my hyperfocus sessions (sometimes on useful, sometimes on useless things) are in between absurd levels of distractions so I can't totally relate.