If dark matter and dark energy are real. While it is generally accepted that they are, dark matter's existence isn't a a closed case yet. Look into the MOND theory.
I personally don't have the education to state a theory with confidence, but I like the idea the physicists saw galaxies rotating in a way which seemed to break the rules of physics they knew and so they said, "our rules can't be wrong, there must be something there we can't see or measure or prove what it is." When it is possible (emphasis on possible) that maybe the laws of physics as related to motion and acceleration are different at scales that include multiple galaxies. Maybe they are rotating at the precise rate they are supposed to and there are undiscovered laws of physics at great scale. They are different rules at the quantum level and we haven't found quantum gravity yet. Is it possible the rules of gravity could be not as concrete at the largest levels of existence? Einstein said large masses bend space and time and we see that as gravity. Could the unexpected rotation of galaxies that is now explained as proving dark matter exists actually be caused by galaxy sized massed bending space and time at a different proportion. I dunno, but wouldn't it be fun if the explanation was so revolutionary and simple?
Disclaimer because this is the internet: I have no clue is this theory could be real, and it is mostly based on other theories by actual, real physicists--which I am not.