Interesting that some ultra-diffuse galaxies don't seem to have dark matter properties.I didn't want to open yet another new thread on such a broad subject. Anyway, the people interested in this subject are already participants and therefore will be duly alerted of this (pseudo-necro)post.
Here's a bit of news that I found astonishing:
https://cosmosmagazine.com/physics/galaxies-without-dark-matter-confirmed
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#The_external_field_effect