This is a touching story and I hadn't been familiar with the details. To summarize, Now And Then (https://en.wikipedia.org/wiki/Now_and_Then_(John_Lennon_song...) had been recorded using cheap equipment (poor quality recording) by John Lennon and handed (on a cassette) to Paul McCartney by Yoko Ono after John Lennon passed away. A higher quality recording couldn't be made because John Lennon had passed but AI technology improvements have made it possible to simulate his voice for a different kind of recording. (The specific song is speculated but Now And Then is what's called out in the article.)

It initially had me thinking this was "just the same thing" as 3D-model Carrie Fisher in Star Wars but, in this case, John Lennon's recorded voice was isolated from the cassette recording rather than a simulacrum of his voice being fabricated. It's an interesting twist on "but is it really $CELEBRITY?" that this is really John Lennon.