It has
sold about 150 million copies worldwide over the past sixty-eight years.
I'm not saying it's unknown, but it's definitely not some huge cultural touchstone. Not until, at least, the Jackson movies.
Don Quixote more than triples the number sold and if you mentioned it in casual conversation many people would have no clue what you're talking about. The first Harry Potter book has sold more than two-thirds the number of books as LotR and it's only twenty-one years old, less than a third the age of Rings.
The books are a previous generations story. More people today recognize the story due to the Jackson movies than the books. If you removed all the Jackson movies from existence and released Rings of Power in that vacuum then it would have only a fraction of the interest it currently has.