17 Nov 20
This isn't about dark matter but rather about what is called the 'missing baryon problem'.
see;
https://en.wikipedia.org/wiki/Missing_baryon_problem
"The missing baryon problem was a problem related to the fact that the observed amount of baryonic matter did not match theoretical predictions"
It is now thought the hidden/lost matter has been finally detected in the cosmic web that is mainly between galaxies via detecting some extremely faint X-ray emissions it produces.