This question could be marked as opinion based or off-topic, but to be honest, there are few places to ask this. There's this question which could be an answer, but I feel it's too related to documentation to answer my question.
Long story:
Since the release of geometry nodes, there has been a lot of relevant hype about them. However, most tutorials go to the extent of only distributing objects. None of the advanced stuff.
Short Story:
What's the best source of learning Advanced Geometry Nodes?
(Should this be a community wiki? In case this question is closed, would someone provide a link to where to ask this type of question? "Blender Artists" might be a good idea but I hardly get replies there.)