Thanks!!! I don't think I added dark background, but I think what affected the background might "Fine Art Photo" in the prompt, and also "Unreal engine 5"
Possibly "Octane Render" got me some dark background. If you're looking for nice lighting I would add "cinematic lighting" or "volumetric lighting". "Dramatic ligthing" could have an effect, or replace it with "creepy" if you want darker.
Also increasing contrast can have a desired effect.