I mean...it really sounds like this guy got seller's remorse after he realized he should have sold his story for more AFTER it got really popular. Should we really be calling it a "nightmare" or am I being pedantic? I concede that the movie industry denying him credit is a dick move but that's not really surprising either.

I only watched this movie because I was stuck on a trans-Atlantic flight with nothing else to do. It was pretty meh - the rom-com elements were terribly cliched. This article made me think the original script would have been a much more interesting film, though probably less commercially successful.

However, the film does have one sequence I really enjoyed. The main character meets the alternative-universe John Lennon, who never became a musician and is living quietly in obscurity. I have always admired Lennon, while acknowledging that he was a flawed person, and so the visual image of a Lennon who lived into old age instead of being assassinated when he was younger was very moving to me.

Thinking about it now, it reminds me of how Achilles "...was either to gain glory and die young, or to live a long but uneventful life in obscurity (Wikipedia)." I often wonder how I would choose if offered that dilemma.

There's a short scifi story someone wrote about John Lennon never being assassinated and how his fallout with the beatles led to him being a homeless nobody.

The name escapes me, will see if I can google, for you might enjoy this one

As somebody pointed out, if John Lennon had not been assassinated, we would simply now have two Bonos.

I think if Lennon wasn't assassinated, he would have drank himself into obscurity

https://www.goodreads.com/en/book/show/17802702-snodgrass-and-other-illusions

the short story is called "Snodgrass" by Ian Macleod

Now I'm kind of glad I never saw it.