Dark matter isn't just a made-up number. It's an observed phenomenon that MOND and other modified-gravity theories cannot explain.
It is an observable fact that dark matter is a distinct substance from baryonic matter. Modified gravity is thoroughly disproven by the many galaxies that have been discovered that have been separated from their dark matter[1], or seem to have never had any in the first place [2]. A galaxy can't be separated from, or be lacking in, something that doesn't exist.
Any attempt to dismiss dark matter entirely without addressing this highly conclusive evidence is not valid.
Its been a very long time since I looked at any of these stuff and I'm certainly not a subject matter expert. I just remember reading about it and the entire idea of dark matter and dark energy came from the fact that the math models they had at the time didn't add up. They needed a way to rectify the math and they did it by saying well if we put this LITERALLY made up number in the equations everything balances out. Then they made up the explanation as to why this number needed to exist as "dark matter/energy" There have been mountains of research made trying to prove this since then that muddy the water of how flimsy the origin was.
It is an observable fact that dark matter is a distinct substance from baryonic matter. Modified gravity is thoroughly disproven by the many galaxies that have been discovered that have been separated from their dark matter[1], or seem to have never had any in the first place [2]. A galaxy can't be separated from, or be lacking in, something that doesn't exist.
Any attempt to dismiss dark matter entirely without addressing this highly conclusive evidence is not valid.
1. https://www.wikiwand.com/en/Bullet_Cluster
2. https://www.inverse.com/science/dark-matter-in-galaxies