Black holes remain an object of mystery for both experts and millions of science fans. Let us dig a little dipper into the unknown in this review. Experts do not understand the state of matter at the centre of a black hole, although it appears more certain (although not entirely certain for all black hole masses, according to some quantum gravity models such as asymptotic safety) that black holes should exist. According to a new review just published, Dr Pinochet mentions: "Given the great interest that black holes arouse among non-specialists, it is important to analyse misconceptions related to them. According to the author, the most common misconceptions are that: (1) black holes are formed from stellar collapse; (2) they are very massive; (3) they are very dense; (4) their gravity absorbs everything; and (5) they are black."
Black holes, almost certainly appear to exist at all sizes both in theory and according to observations. (A black hole hasn't been created at the lab yet as the energies required are too high). In particular we know about mini black holes with the size of an atom, stellar sized black holes, and huge black holes at the centres of the galaxies. Among these 3 categories, there exist strong indirect observational evidence for the last two categories, but mini black holes haven't yet been observed (according to quantum theory they should have a very short lifespan and evaporate emitting gamma rays). Neither of course LHC succeeded in producing mini black holes, although there was a hope according to some theories.
Reference: https://arxiv.org/pdf/1909.06006.pdf