The devil wears Max Mara in “The High Note.”

Shift the style-obsessed mean boss from the fashion world of “The Devil Wears Prada” to a style-obsessed mean boss from the music world and you have “The High Note” — except not as funny or insightful. Weirdly, it’s the second “Prada” knockoff in a row for Nisha Ganatra, who also directed last summer’s “Late Night,” which was “Prada” in the TV world. If someone feels inclined to make a comedy about a vicious grain-elevator manager who rips her assistant a new one every time she brings her a tepid latté, I guess Ganatra is their woman.

The chief asset of “The High Note” — as with “Prada” and “Late Night” — is its sharp-tongued gorgon. Tracee Ellis Ross (“Blackish”) slides stylishly into Meryl Streep’s and Emma Thompson’s pumps as Grace Davis, a high-strung pop star. It’s a symptom of the generic quality of “The High Note” that it’s impossible to get a handle on what sort of pop star Grace is supposed to be, since she has the Vegas residency and lack of recent hits of a Celine Dion, but the backup dancers of a Jennifer Lopez and the confessional instincts of a Fiona Apple.

Ross may not have the stage presence of her mom, Diana Ross (who does?), but she can sing, and as her witty asides, quirky nonverbal sounds and wide array of knowing looks demonstrate week after week on TV’s “Blackish,” she is more than ready to play the lead in a movie comedy. She makes Grace’s insults hilarious and just mean enough to stay on the right side of us hating her. Unfortunately, Grace is not the lead character in “The High Note,” even if an improbable, late-breaking twist would like us to think so.

The lead is Maggie (Dakota Johnson), a latté-fetcher who wants to be a producer, an important music industry job that is not easy to depict on screen since it mostly appears to involve twiddling knobs. Johnson also has verified sitcom chops, as demonstrated on her short-lived “Ben and Kate,” but she’s not asked to be funny in “The High Note.” Instead, her character is meant to weave together far too many plot strands, which include her relationship with her musician dad (Bill Pullman), age discrimination, two career arcs, boyfriend issues, the aforementioned twist and cultural appropriation. The latter is an especially awkward subject for a movie whose white heroine at one point is required to tell a black vocalist how to sing a Sam Cooke song.

Ganatra’s work with actors is impeccable. Not only are Ross and Johnson able to make the material seem better than it is, but so are Zoë Chao, who has slid into Judy Greer’s Hilarious Best Friend parts (“Downhill,” “Where’d You Go, Bernadette?”), and Pullman, playing a Don Henley-ish character who is definitely not Henley, since Flora Greeson’s script says very mean things about him.

That script is the main problem in “The High Note.” It really goes off the rails in the final half-hour, when nothing makes any sense and it becomes clear that the devil is in the details.