What happens when Brat Summer — that slime-green cultural phenomenon in which Charli XCX dared us to all be much messier, much less apologetic, to send that first text and not regret it — really ends?

The British pop star, whose sixth studio album became a cultural and commercial phenomenon synonymous with an attitude of spiky independence in 2024, is moving on to a new passion: film.

“This movie is about the end of an era,” Charli said when she entered the building, telling the crowd she was honored to premiere in a year when Sundance itself is leaving its longtime home of Park Ci...