How is matter stored in black hole?

A black hole engulfs the matter nearby, how does it store the mass inside? We know that matter is composed of particles, does a black hole store the mass in massive particles? Or can we assume that it's composed of extremal black holes? what are theories about it?

EDIT: I checked out Black-holes are in which state of matter? it doesn't provide a definite answer.

The inside of a black hole is speculative, certainly at the singularity (if there is one), for the unknown local geometry of spacetime. Adding mass to a black hole linearly increases its external radius. The external volume increases as the cube of the external radius, implying that galactic core supermassive black holes have average densities approaching zero. NGC 4889 is 2.1×10^10 solar masses, then $r = (2.95)(M/M_{sun})$ km. The sun's average density is 1409 kg/m^3. Calculate NGC 4889's average external density.
Consider a Kerr (rotating) black hole. If mass resides in a central zero-dimensional singularity, what sources the external angular momentum? $L= r × mv$. Black hole interiors are not well-defined.