Well, the story of 'Us' is centered around a family who encounter their doppelgangers and uncover a sinister conspiracy lurking beneath the surface. It's full of suspense and surprises.
Well, not all US movies are based on true stories. Some are purely the creation of the filmmakers' imagination. But when they are based on real events, they might tweak certain details for dramatic effect or to make the story more engaging for the audience.