I'm not quite sure how this would manifest, or how to explain this, so sorry if this is a bit confusing! I will try my best with some examples.

I think it would be cool/helpful to have a section somewhere that tells us what kind of book we're reading in terms of sub-genre. I understand having a bunch of genres can be hard to read / clog up the UI but maybe it can be user-based? And when we're filling out those little surveys when we rate books we can tell other users "This is a gothic horror book." or "This is a survival thriller." or "This is a cozy mystery." or "This is an urban fantasy." etc!