There is a course in the Moodle Development School here: https://moodledev.moodle.school/course/view.php?id=3.
This is quite interesting although clearly a work in progress.
I was working through it and got stuck in a couple of places so I wondered if anyone has actually completed the assignments and has code available on GitHub? For example, whoever wrote the assignments
Without code it's easy to make a small mistake which doesn't show up until further down the track.