There are galaxies that should have dark matter to explain their existence but they do not.
"Mystery of Galaxy's Missing Dark Matter Deepens | NASA" https://www.nasa.gov/feature/goddard/2021/mystery-of-the-galaxys-missing-dark-matter-deepens
"This weird galaxy is missing all of its dark matter and scientists can't explain it | Space" https://www.space.com/dark-matter-missing-from-galaxy