It's not that clear cut. If you work for Amazon, they claim all of your IP -- everything they are in the business of. Amazon produces movies, books, products. It's not just code.
That said, "they claim" might be leagues away from "what they could win in court", but they still try.
I have published novels and awhile ago an Amazon recruiter reached out to me for a tech role on a team building story tracking software.
It never went anywhere but I did wonder at the time how they view employees writing their own novels or movies etc. For example, would they have any possible claims on any future novels based in those existing worlds and characters in my previous works.
Obviously they have the funds to outlast you in any claim if by small chance you happen to have a hit at some point.
That said, "they claim" might be leagues away from "what they could win in court", but they still try.
Supervillain shit.