It doesn't have a great anime adaptation, but you might like the Devilman manga. If it has to be anime, Devilman Crybaby is still fine, but not nearly as emotionally impactful, and with worse designs and weaker themes/imagery.

Psycho Pass is a future-crime show that's fairly dark, but also fun.

You'd probably like The Promised Neverland.

Death Note's probably up your alley. I recommend manga over anime for that one too.

Berserk, though I'm not caught up nor do I remember how much I've actually read, so Idk how it holds up. Everyone else seems to think it's dark and great.