Immersion, and time
Reading vs understanding
We can read very fast. But understanding takes time.
Years, if we're lucky. And it is never clear if the understanding is complete either. One could say that there is something new to learn always, but that's a cheeky substanceless wit: I do sometimes reach points for very specific things where I understand them, and more information about them is noise at best.
So, for very specific domains, there is an end. But that end takes time. At least a couple of order of magnitudes more.
Sometimes, one can understand at the speed of reading, but that is only when one has already understood all the prerequisites.
A younger me used to think that one can only understand books that one has already understood subconsciously. That is, the purpose of the written word is to make the understanding manifest, but the understanding itself is not coming through the words.
I now think that is incorrect. If one has understood the necessary prerequisites, sometimes a sentence is all it takes to unplateau to the next plane of understanding.
I haven't found shortcuts to understanding.
Since it takes too long, sometimes I indulge in rituals, e.g. writing things down, by hand, on paper. I don't know, one way or the other, if it helps in the understanding, but it is just a ritual nevertheless to pass the time. Many smart people I've met seem to understand quicker, and without external ceremony. It takes much longer for me, and the only way seems to be immersion. Years of it.
Immersion, and time.