What do you think of this, still very speculative, Carlo Rovelli&Co.'s idea?

In short: during its evaporation, a Black Hole would reach a point when he cannot shrink any further because space-time is “granular” (according to loop gravity theory), so cannot be squeezed infinitely, and rebound to form a White Hole.

White Holes would be very tiny, but much bigger in the inside, lacking electric charge, not emitting radiation, invisible (nor emitting or reflecting light and also far smaller than a wavelength of light) and only capable of gravitational interaction, because as “reverse Black Holes” they cannot swallow anything.

So, an enormous number of primordial Black Holes, that had time to “die” and become microscopical White Holes, would be what we call Dark Matter.

(The theory goes beyond that, to the Big Bounce hypothesis, suggesting some of those White Holes would predate the Big Bang as “survivors” of the previous Universe)