[altgeek]

Guitar-related, Tommaso Zillio (https://www.musictheoryforguitar.com/abouttommasozillio.html) is pretty good for intermediate to advanced topics. I haven't looked at his courses; I use him for more composition ideas.

Signals Music Studio is also thought provoking for ideas (https://signalsmusicstudio.com/) ; check out his incremental approaches to writing with the Locrian mode.