The movie was based on a fictional novel. The book, Blonde: A Novel was published in 2000. The author, Joyce Carol Oates has very clearly said that while the "subject" (Marilyn) was real, her book is totally fiction.

She said she was "imagining" a different Marilyn. So basically, just another day in Hollywood and more people cashing in on Marilyn's name. I'm disappointed Netflix got on board