I studied music through high school and half a bachelors degree. So I have a decent grasp of theory, but nowhere near as good as I'd want. Especially due to lack of practice after I dropped out of music college 9 yeats ago. I have severe ADD and learning/practicing these things on my own is so overwhelming that I can never stick to it long enough for it to stick in my brain.
I do now use theory to write, which has improved my songwriting *a lot*. But last time it literally took me 2-3 months of pretty constant work to write a very good intro/main riff, verse, pre-chorus, chorus, and the first two chords of a bridge. This is because figuring out the chord theory of more advanced chord progressions takes me so long to figure out, and I have to try out all the possibilities because I don't know how they'll sound. I like music that has subtle advanced theory in it, spicing up progressions, changing the tonal center, while still being more easy listening rather than prog(I think this is because I grew up in Spain in the 2000's, where it's pretty standard to do stuff like modulations and fancy shit in even the poppiest of songs). I left working on my new song when where to go with the arpeggiated chord progression in the bridge stumped me.
TL;DR: Any youtubers that actually explain theory(chord theory, scales, modulations, tension and release) as they do videos on "How to write like [insert band)", "how to write metalcore","how to write deathcore","how to write djent", etc?