Yes, black holes and other compact objects have pretty much been ruled out as candidates for dark matter. The issue is that they would produce gravitational mi

Yes, black holes and other compact objects have pretty much been ruled out as candidates for dark matter. The issue is that they would produce gravitational microlensing signals which are not observed. In brief, when the black hole passes in front of a star, its gravitational field magnifies the light from the star in a characteristic way. By analyzing the shape of the light curve, you can figure out pretty much everything about the system like the masses and the distances. Systematic surveys for these microlensing events like OGLE have not observed black hole microlensing events at the rate that would be needed for black holes to constitute most of the dark matter out there. They do observe quite a few planetary microlensing events, though.