OK so if [STRIKE]anything[/STRIKE] something [STRIKE]which[/STRIKE] is non-living and cannot possess anything, we can't use "'s" for that thing?
We didn't say that. You have already been given the example "Gravity's cinematography was phenomenal". That is a correct sentence. However, the specific example you gave with the film "Rocky" and "sequel" doesn't take the possessive.
There have been three Rocky sequels.
There have been three Star Wars trilogy prequels and there will soon be three Star Wars trilogy sequels.
Have you read the Lord of the Rings sequel?
With books and films, we don't use the possessive when talking about prequels and sequels.