I don't think that I have ADHD, but at times I just have to re-read a sentence a couple of times to grasp its meaning. Or rewind 30 seconds in a podcast or audiobook to listen again.
If this happens too many times in a row, I assume I'm tired, so I switch to a more manual task (like doing the dishes).
I remember times when I just had to study at that moment. I would force myself to re-read sentences until they made sense. I would rephrase the sentence or read the same sentence in another language that I know, until it made sense. I could spend the whole afternoon focussing on just a few pages. But I think it was a good exercise. I think focus is like a "muscle" that can be trained a bit.
You can be diagnose with ADHD for any number of circumstances, the ADHD diagnosis is not based on a specific cause, only on specific symptoms, it doesn't matter where the symptoms come from exactly (circumstance? nutrition? neurodivergent in the wrong environment? etc).
I feel the same way you do. Something else to take into account:
A lot of people are just mediocre at explaining themselves. This is fine because sometimes the information they have is good, the medium of communication is shabby, but we can still do an extended effort and look past the medium in order to get to the information. The point being, if someone is really adept at communication then you might find yourself focusing on really complex topics with ease, because it is engaging and nicely laid out. OTOH if I hand you an IKEA manual to build a simple vase but the scribbles are tiny and confusing, you will be like "Woah this is so difficult to pay attention to!".
Happens to me sometimes too. And I don't have ADHD after testing. Choline and other focus related supplements helped a bit. Aggressively trying to reduce anxiety helped more than anything. Anxiety disconnects the "now" from the "goal" states and can massively disrupt concentration.
Could be anxiety, could be bad habits. If it's possible, better to go to ask to specialist just in case - not much to be lost, and you gain internal peace.
If this happens too many times in a row, I assume I'm tired, so I switch to a more manual task (like doing the dishes).
I remember times when I just had to study at that moment. I would force myself to re-read sentences until they made sense. I would rephrase the sentence or read the same sentence in another language that I know, until it made sense. I could spend the whole afternoon focussing on just a few pages. But I think it was a good exercise. I think focus is like a "muscle" that can be trained a bit.