Joe Alwyn was officially recognized as a producer of Taylor Swift's “august,” alongside Swift and Jack Antonoff.
Swift and Antonoff wrote the song and produced it, while Alwyn was later recognized as a co-producer. Alwyn worked on several Folklore songs under the pseudonym William Bowery, although the “august” credits identify him by his real name in the song's production information.
The credit became notable after Folklore won Album of the Year at the 63rd Annual Grammy Awards. The Recording Academy recognized Alwyn's contribution, adding him to the album's Grammy-winning producer credits.
Aaron Dessner is another important Folklore collaborator, but he was not the answer to this question. Dessner produced numerous songs on the album, while “august” specifically credits Swift, Antonoff, and Alwyn. That distinction is useful because the album's large creative team can make individual song credits easy to confuse.