It just occured to me that you're probably talking more about the study of creating the art. But I already wrote out this post so here you go!
A couple of youtube channels I greatly enjoy in the study of art composition, background, and history are
- Great Art Explained. I first encountered this channel in an A to B to C starting from a Dunky video on the movie Playtime to my long fondness for Edward Hopper's Nighthawks and later recalling this analysis when I played through the jazz-filled adventure puzzle game Genesis Noir.
- I'm just really into that Art Deco style, and when you think great art of course you think Magic the Gathering cards. Rhystic Studies has amazing breakdowns of both the story and art of MTG cards, like my favorite video on the art of the art deco inspired Streets of New Capenna set