My Marianne

In the Netflix movie "Eurovision Song Contest: The Story Of Fire Saga" the role of "Sigrit Ericksdóttir" was played by actress Rachel McAdams, but the artist/voice behind the songs is actually Molly Sandén (full name Molly My Marianne Sandén), who McAdams lipsynced to. Will Ferrell (the other lead role of the movie) on the other hand performed his vocals himself.

From a Vanity Fair article:

According to Netflix, Sandén’s vocals were mixed with McAdams’s own voice for the tracks. In a separate phone call with Vanity Fair, Eurovision’s music producer Kotecha said that Sandén and McAdams’s “tones worked so well together” that, in playing back certain tracks, he had a hard time differentiating between the vocals. But Sandén, who has seen the film, said she only noticed McAdams’s voice in a scene in which the actor was singing to herself in front of a piano. Asked if she thought the vocals had been mixed, Sandén sounded skeptical: “If they say so, maybe that’s the truth. But I just know that I didn’t really hear in the soundtrack...maybe it’s mixed in somewhere.”