It's very unlikely, as black holes are remnants of stars greater than 10 sun masses that gone supernova, and it's very unlikely we'll ever have a black hole in our solar system, so if Planet 9 exists, it's more likely a planet than a black hole.
There are some dark exoplanets NASA found out there, the darkest being TrES-2b, which recieves almost no light from its star, making it the darkest planet ever found.
So Planet 9 could be one of those dark planets similar to TrES-2b, but smaller, which could explain why we couldn't find it, and has an almost Uranian mass affecting the orbits of dwarf planets without it being a micro black hole.
Besides, Scientists believe it has a radius comparable to that of Neptune.