Yes it's got a million subscribers but it's still underrated.
It's called tale foundry. I don't know what this guy's background is but he combines a depth of literary knowledge, insightful personal observations, with a broad reading of fiction, fantasy, myth, and science fiction to examine the different aspects of literature. Themes, types of characterization, plot devices, and many of the other features of writing that make stories good and intriguing and most of all relevant to us.
I think part of why it's not more popular and why I like it so much is its gentle low-key style while at the same time being intellectually and emotionally challenging. There's nothing sensational or bombastic about it. It's just a lot of heartfelt observation and pontification on the elements of storytelling and how it contributes to our understanding of The human condition.
He does a good job covering horror and dark themes, but that is not his exclusive focus. Just go over to the channel and look up whatever topic seems of interest to you and I think you're in for a pleasant surprise.