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.
This was the mindset that drove Harrison out of The Beatles. I might have the anecdote wrong, but what I gather was Lennon was always the band’s leader, but when he started to “check out” (as someone put it, he basically “won the lottery” as far as fame and fortune and was distractedly in love), McCartney stepped up to “substitute lead” and was a bit overbearing. Harrison, being largely ignored and dismissed finally said “I’m done” which served as a slap Lennon and McCartney needed.
McCartney has a hubris which never changed. I am fairly certain he truly believes that he is doing the right thing and that George would have approved if he could have heard the recovered vocals.
I just don’t know if this could truly be a “Beatles” song, “Yesterday” notwithstanding, without some input from George as well, but I can’t see that happening - it would be a monumental coincidence if there was some track Harrison had that somehow dovetailed into an unfinished fragment of a track Lennon left behind. The only way I could possibly see it is if Dhani Harrison is somehow involved to speak on his father’s behalf.