I find a similar pattern at work for myself. Although I think I've finally accepted that I lose interest in whatever I'm hyper focused on right around the time additional progress can no longer be made merely by what I would describe as the advanced dabbling, DIY pattern recognition and puzzle solving reward cycles delivered by straight ADHD style hyperfocus, but instead only happens by applied and sustained structured learning techniques as well.
A mathematical example would be right around the point where one finds that the delightfully focused exploration/experimentation afforded by ADHD which carried you to self-discovery of, say, why SIN relates to COS through their derivatives, or through the Pythagorean theorem, doesn't actually get you very far in calculus unless you intend to re-invent, at great personal cost and to no practical advantage, a lot of very well-known wheels.
Instead you need that hard-won scaffolding of rote memorization, the almost muscle-memory capacity for sight-recognition of a couple dozen identities and theorems and familiar problem forms, to get much further.
Spontaneous yawning when you're wide awake and actively interested in what you're reading or learning is for me a telltale sign that I have reached the point where I'll I have to tack a frustrating zigzag course _against_ the ADHD winds instead of sailing with them.