The audio of John Lennon's demo-tape from the 1970s was separated with the use of AI-separation technology that isolated the track (there was ambience in the tape that couldn't separate John's voice without sacrificing the overall quality). This wasn't possible back in 1995/'96 when the then three surviving members of The Beatles tried releasing the song as a possible third reunion single. However, the song was still worked on up to its release in 2023; the Beatles worked on the stuff around John's voice until the technology could salvage his voice in a satisfactory manner.
The only UK number one single by The Beatles whose composition isn't officially attributed to Lennon-McCartney.