These YouTube tutorials are by someone new to me on YT, and the Jazz overview is one of the finest music theory videos I've seen. It's pretty rapid fire, but well worth pausing and considering.
The information on the tritone in the major scale and how it's notes define diatonic chords which are dominant or predominant, is frankly amazing to me! Great description of what gives chord families their characters, and what modifiers to look out for.
I shall need to keep checking out this guy's material.