Dark matter IS a theory. From the article you linked: >Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in obs

Dark matter IS a theory. From the article you linked: >Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws and quantum gravitational laws.[11] Whether something is a theory or not has nothing to do with whether it is real, however.