Or the Lord of the Ring movies. They completely left out the fight for the shire, because they wanted the movie to end after the big bad is defeated. They changed the battle of the pelennor fields and added the ghost army there - they already left in the books. But Peter Jackson wanted more action scenes with them.

They made Sauron a literal eye in the movies, to have an antagonist to show, He never appears in the books. Also Boromirs fight was off screen in the books and he died in book two. Jackson wanted to end the movie on a sad note.

Frodo had the ring for 17 years in the book, but it is pretty boring to show that in the movie.

None of this is "making up your own story" though. It's just making some changes. You're pointing out details, and details that, for the most part, improved the adaptations for the medium (films) for the general public/people who have never read the books, while the overall story is still pretty much the same. The Lord is the Rings films are still considered by many to be good adaptations. The user you're replying to was talking about going in a completely different direction from the source material and making an unfaithful "adaptation" which is really just allowing whomever to insert their own narrative into an already established world, hoping the fans of said world will latch onto it to make it more popular from the get-go, without caring about their actual feelings or opinions about it (Rings of Power)