Some cuts from LotR obviously had to be made for the movies. Tom Bombadil is the one people mention, and it’s obviously. He and Goldberry just wouldn’t translate, and the mystery of them would be lost. Those two characters wouldn’t work in film.
But another area that should be cut is the ride from Minas Tirith to the Morannon. That just wouldn’t work in a movie as long as it is in a book, because movies need a bit more focus. That long sequence of exploration and travel is world building. It’s development. It’s character. It’s way too long, and should be cut down to two or three short cuts, like in the movies. If you want more of that, the books are the place for it.
P Jackson did that right.