The heaviest elements known in abundance in nature are forged deep within stars.
These elements are made possible by the high densities/pressures within the stars.
Black holes are known to have a much higher density/pressure than any known star.
Black holes are also known to be a phase of stellar evolution - this suggests that the original star's internal process of forging metals would persist within the resultant black hole.
Scientists have forged synthetic/ephemeral heavy metals under conditions which could hypothetically be sustained within a black hole.
Black holes forge heavier elements that have not been observed on earth. The conditions needed to sustain these elements are unique to the black hole, due to its high density/pressures. These conditions can be glimpsed, but not sustained in any experimental context
Follow up questions:
Has this been hypothesized?
Where can I find research on this topic?