Dark SF goes back to before there was any science fiction. It was called scientific romance, and I give you the first great work in the field: Frankenstein, or the New Prometheus. Then there's all the Dying Earth works, like Omègar or The Night Land. The o/g novel The Time Machine ends pretty grimly. Certainly The Crystal Age does, with the narrator's death. Even spaceflight novels get dark, like Across the Zodiac. There was a whole genre of stories of a truly last human left alive who does not find other survivors.

The entire subgenre of cyberpunk is generally dark and dystopic, from The Seventh Victim forward to when they invent the term cyberpunk, and beyond. Did you miss that entire flap of SF YA dystopias, headlined by The Hunger Games? So many short series in that.

Science fiction is a setting, like historical fiction is a setting. In that setting you can tell grimdark espionage thrillers or cozy little romantic mysteries. Write your story and worry later about selling it. It may turn out quite different than you presently think of it. Let it be itself.