

I do research on dark matter, and one of the more interesting possibilities I have heard is that these black holes could in theory be formed by directly collapsing dark matter!
There’s and increasing amount of attention being spent investigating a slight modification to the standard Lambda cold dark matter cosmology, by allowing dark matter to have a little bit of self-interactions. These can then allow part of a larger dark matter halo to directly collapse into a black hole.
It’s possible primordial black holes could be dark matter, but there’s only a certain mass range allowed, roughly around the mass of an asteroid, for example.
But somewhat confusingly, these would be poor candidates to seed these massive black holes.