Good question. for django internals it is the official link https://docs.djangoproject.com/en/dev/internals/
django use meta programming a lot in its ORM & Form & Admin.
to understand django public API's you need to first understand meta programming & meta class in django.
For understanding how to use the django ORM properly you can check this playlist https://www.youtube.com/watch?v=iQF6pln3Gog&list=PLOLrQ9Pn6cazjoDEnwzcdWWf4SNS0QZml .
For understanding django models internal meta API this video is a good start, though it might seem too advance at first:
https://www.youtube.com/watch?v=VgM0qmpHDiE
I will be adding more relevant links to my answer.
Also for advance level deep understanding of the internals of django components this conference website has slides and videos both to increase your depth in django https://djangounderthehood.com/
And all the videos can be found in this link https://www.youtube.com/@djangounderthehood420/videos