I think His Dark Materials by Philip Pullman could be considered dark fantasy and it’s one of my favourite series ever. It incorporates some biblical elements, common fantasy elements, some science-fictiony effects, and so many liminal ideas and epic characters. One of the what villains ever written also, in my personal opinion.
Also, Miss Peregrine’s Home for Peculiar Children by Ransom Riggs and the rest of the series has a really twisted sort of aesthetic with awesome photos as part of the story. Love the characters, love the universe, love the overall effect.
There’s this one-off that, in all fairness, I read when I was eleven, but I remember loving it. It’s called the Path of Names by Ari B. Goelman and I think it is described as a children’s novel. It had elements of Judaism and horror I think. Anyway, look into if you think it could be good.
There’s a book I studied in class called The Bloody Chamber and Other Stories by Angela Carter, super gothic and weird and so so so good, it’ll leave you confused and thinking about for weeks, I loved it so much.
Dark is a show that I didn’t finish because it wasn’t my thing but it fits perfectly into the dark fantasy genre, it’s a bit about time travel, a bit about death, I don’t quite remember but anyway.
Inception is a movie that’s maybe limited in fantasy but still really good, and I’d call it dark in the gothic sort of sense with its reliance on obscurity and confusion and liminal ideas.
There’s The Haunting of Hill house and The Haunting of Bly Manor that are really, really excellent. It’s basically horror but I found it more emotional than scary, and the fantasy elements are really well-scripted and I just love them both (maybe hill house more).
I won’t bother recommending The Magnus Archives podcast as in I’m sure you’ve heard of it.
That’s what I’ve got so far. I’ll see if I think of anything else by the time I get home. Hope this was useful :)