Since Sept 2019 there's been some speculation1 whether the hypothetical planet far beyond the Kuiper belt is actually a primordial black hole. It would be the closest black hole to the Earth (500 au from the Sun on average) and we might send a probe there.
I've already discussed the speed needed to enter the black hole on astronomy.SE and a user (don't remember who anymore) concluded that the probe must enter at close-to-light-speed in order to not get spaghettified and torn apart. And since the black hole would have a diameter of about 2 inches (5 cm) the probe must be very small of course, with the camera on its peak, so that it enters the black hole camera-first. The probe probably would consist only of a camera.
Is it realistically possible to achieve a speed of 0.95 c for a probe (perhaps Breakthrough Starshot with a swing-by on a star) and what else would it take to make the probe safely fly into the black hole? And might it be risky because a man-made probe might exit the black hole in another location and/or time?
Perhaps I should tell you that it doesn't matter whether the speculation is true. The question is what it takes to enter it, so just assume there is a primordial black hole.
1Gizomodo's What If Planet Nine Is a Bowling Ball-Size Black Hole? links to the arXiv preprint What if Planet 9 is a Primordial Black Hole?