Assuming the mass of an electron is contained in a volume greater than zero (and thus NOT a point mass), what is (are) the measured and/or calculated density (or density ranges) of an electron?
How does the density of electrons compare to the density of "black holes"?
I'm a mechanical engineer, not a physicist, so please give me the simplest answer which does the topic justice at a freshman college level (not a PhD level).
No experiment has been able to measure the size of the electron. If it has a radius, it is smaller than the smallest size we can measure. In that sense, it is indistinguishable from a point particle.
On the other hand, to be so dense that it collapsed into a black hole, its radius would have to be about the size of the Planck scale, $10^{-35}$ m. No experiment has been done anywhere near that scale. We don't even have theories on that scale.
On the other other hand, it is wrong to think of the electron in an atom as a tiny point particle orbiting the nucleus. The electron is like a wave. It is spread out. It has no position or size. It is attracted to the nucleus, and is more likely to be found nearby. But that confines the electron to a small region. As the uncertainty principle says, that necessarily makes the uncertainty in the momentum large. An electron that may have a large momentum isn't likely to stay near the nucleus. These two competing uncertainties set the size of the region where you are likely to find the electron.
It isn't like a classical particle and you just don't know where it is. It has no precise location. Like a wave, parts from different regions can interfere with each other, changing where you are likely to find it.
For more on this, see Does the collapse of the wave function happen immediately everywhere?. It is a different question, but the answers discuss this idea.
