"The key is to keep rep counts in each set manageable — generally under 5; in some rare cases up to 10. "

Just from a pure fitness perspective, I want to highlight that you've introduced a logical issue here.

If you're actually training with intent to grow the muscle and increase strength, sets of 5 presume a much higher weight than sets of 10 if you're talking about the effectiveness of the training. You don't train with a set of 5 with a weight you can lift 10 times. Likewise, you don't want to do sets of 10 with a weight you can lift 20 times. This is what's known as a colossal waste of gym time.

The logical issue you've introduced is that you need to be able to introspect your "reps in reserve" to even know what the appropriate weight to lift 5 times would be.

There is nothing, in my experience, about people with ADHD that makes them less able than neurotypical people to understand reps in reserve. It's a skill anyone can develop over time -- and actually, I think people with ADHD develop this skill much more quickly.