Richard Feynman having the quantum Hall effect on his "to learn" list is amazing. I mean, it makes sense, because less than three years before he died the Nobel Prize in physics was awarded for its discovery. But it shows that even one of the greatest physicists of his generation had not fully grasped something that is now part of every undergraduate physics degree's standard curriculum and is arguably much less comp…
I think there is some huge difference between learning some bleeding edge ideas vs stuff that -for years - has been repackaged, processed, and optimized for being taught and for making exams out of it.
The thing is, most of Feynman's work (in particular the stuff he received the Nobel prize for) has not really made it into undergraduate courses, despite being decades older and going through a lot more repackaging and processing. But the quantum hall effect is so simple by comparison that it is taught in early QM courses. So the key takeaway here is that there were still pretty low hanging fruits in physics two decades after Feynman won the Nobel.