Here are two YT resources which I found most helpful as novice (not having any formal education on music theory). They both destill the essence of diatonic harmony. I found that this basic learning content blends very well with what Scaler can offer.
I watched both pt 1 and pt 2 of these videos and can thoroughly recommend them . Although pt 1 is a bit long, > 1hr, and the presentation style may sem a little bit repetative, overall the explanation is easy to follow.
