Who or what is being described by the term “Elohim” used in Genesis 6: “The Nefilim were upon the earth in those days and thereafter too, when the sons of the Elohim cohabited with the daughters of the Adam and they bore children unto them,” and what does this verse truly mean?

This verse truly is describing the interbreeding of Anunnaki Gods, as they were viewed in those times, with human females to create hybrid beings and maintain an Anunnaki lineage. This was done through simple exploitation at the outset but was soon seen to have some interesting benefits of its own. And then, the lineage was supported and allowed to continue as a kind of ego extension, somewhat like a hobby but totally for selfish reasons and selfish purposes, to leave their stamp on things and to create a state of interdependency that was irrevocable. So the term Elohim, in this context, means "Supreme God‑level Ruler" and was not referring to Creator but to the gods of the time, the power hierarchy of Anunnaki present and engaged as active overlords of human civilization at that point in time.