The title is misleading. McCarney used machine learning to isolate Lennon’s vocals from a badly recorded demo tape - one that the group (largely at Harrison’s request) abandoned during their “Anthology” recording sessions.
Kind of melancholic as this will be the last Beatles song, and not even the entire group, as it was never fully worked on, I don’t know if there are guitar tracks by Harrison that could contribute to this song.
I see it more as one last farewell, taking advantage of the advances in technology. Apparently the Get Back movie inspired this move, as Peter Jackson used machine learning to isolate the dialog. The song McCartney chose was one he really wanted on the first Anthology album, but the sound quality was just too bad. It’s possible that reclaiming this song never left his “bucket list.”
A part of me wonders if the surviving Beatles ever regretted never making the overtures to “reunite” when the could have, especially when there was a renaissance of band reunions some time after Lennon’s death, and there is now something of a “renaissance” as the younger generations rediscover older music.
For me, The Beatles were always in the music background - much of their later material were mainstays on classic rock FM stations when I was a kid. Now folks who have only known streaming are rediscovering this band (and others). Back on the Reddit there was a dedicated subreddit for The Beatles, and it was always a delight to see “kids” discover the band. As an old person, it’s kind of surreal to see modern technology and a mid-20th century band generate new music, but for the Beatles, this is pretty much on-brand: much of their music was pushing to see what they could do with the latest and greatest advances.