Last week, the actress Elle Fanning arrived in New York for the première of “Margo’s Got Money Troubles”—a black comedy brightened by its colorfully tacky Orange County setting and by the sparkle in her performance as Margo, a nineteen-year-old single mother who begins making “camgirl” content on the adult-entertainment website OnlyFans to pay the bills. “I came from Budapest!” she exclaimed, in a...