I wish @heyeased was able to do a magic 'jet black' magic wallpaper to remove the grayish area around the dock, but he said it wasn't possible at that time. I wonder if he was ever able to do it?
I haven't seen one. The only one he has that hides the dock is a dark gray. I had saved a bunch of his older ones going back to iOS 10. Some actually look good on iOS 14. No black hide dock though.