The velocity curves of galaxies do not obey Newtonian gravity. Solutions such as "dark matter" and "Modified Newtonian Dynamics (MOND)" have been proposed. But no candidate for dark matter has been found, and MOND is not a relativistic theory.

"A model of galaxy based on a general relativity metric was also proposed, showing that the rotation curves for the Milky Way, NGC 3031, NGC 3198 and NGC 7331 are consistent with the mass density distributions of the visible matter, avoiding the need for a massive halo of exotic dark matter."

"According to a 2020 analysis of the data produced by the Gaia spacecraft, it would seem possible to explain at least the Milky Way's rotation curve without requiring any dark matter if instead of a Newtonian approximation the entire set of equations of general relativity is adopted."

"In March 2021, Gerson Otto Ludwig published a model based on general relativity that explains galaxy rotation curves with gravitoelectromagnetism."

https://en.wikipedia.org/wiki/Galaxy_rotation_curve