I went for a walk and had a conversation about Rademacher complexity and VC-dimension of a classifier, then I asked it to quiz my understanding based on what we talked about. It's almost at the level on "Her" but you have a very knowledgeable tutor to ask who won't judge and is always available.
Until ChatGPT can store and reference all past conversations, I'd suggest asking it to generate flashcards for e.g. Anki. I've mainly used it when I want to understand or deepen my understanding of something pretty specific.