While the onscreen title in the actual film is Dune: Part One, the trailers and posters and other marketing materials all refer to it simply as Dune.
Villeneuve’s Dune (Part One) ends with Paul (Timothee Chalamet) and his mother Lady Jessica (Rebecca Ferguson) venturing into the Arrakis dessert with members of the Fremen, the planet’s native people.
That’s the slightly cheeky final line of dialogue in Dune — or, as the onscreen title card reads, Dune: Part One.
Again, what comes next in Dune: Part Two could differ from its Herbert’s concepts, perhaps in large ways.