Most pagan polytheistic societies have monotheistic concepts embedded in them, and the more philosophical people in pagan societies tend to think of either all the gods being ruled by one ruling god or Creator, or that all the gods, or a few of the most powerful gods, are fragments of a sort of absolute godness. Many Egyptians associated absolute godness or rulership with certain famous gods like Osiris (who ran the good bits of the afterworld), his wife Isis (who brought Osiris back from the dead), Amon/Ra (the god of the sun), Horus (the son of Isis and Osiris), or so on.
In Egypt specifically, there was an extreme case of this with the Pharaoh Akhnaten, who decided that the real God was Aten, the disk of the sun. He ordered everybody in Egypt to worship Aten and turn away from all the other gods, and tried to totally remake Egyptian society to go along with this. After Akhnaten died or disappeared, the priests and kings afterward ritually obliterated his memory, but he was still pretty famous as you might imagine. (And everybody knows about his wife and queen, the beautiful Nefertiti, and his son, Tutankhamun.)
There’s a lot of debate about when Joseph and Moses come along, relative to Akhnaten. As you might imagine.
Well, midway between polytheism and monotheism are
henotheism (worshipping one god but not denying that other persons can with equal validity worship different gods),
kathenotheism (the worship of one god at a time, treating each of them in turn as supreme) and
monolatry (the recognition of the existence of many gods, but with the consistent worship of only one deity).
A few folks would even argue that the earliest Israelites were strict monolatrists (in other words, they worshipped Yhwh alone, but did not preclude the idea that other gods - who in turn were
not to be worshipped - existed) before this belief was further refined into full-fledged monotheism. Same goes for Akhnaten: the details of Atenist theology are still unclear, but as he did not actively deny the existence of other gods but simply refrained from worshipping any but “
Re-Horakhty (Re (who is) Horus of the Horizons) who rejoices in his name of Shu-who-is-in-the-solar disc (Aten),” aka the
Re-Horus-Aten or simply the
Aten (promoting him first as the supreme god, and then as the
only god worthy of worship - by him, that is; the common people would in turn homage him as the mediator), some interpret him - or at least him in the first stage of his religious reforms - as being in reality a hard-line henotheist or monolatrist (the only god - for Egyptians, that is) rather than a true monotheist.
What we do know was that the Israelites’ neighbors in Canaan were more or less henotheists, or at least were moving towards it: each people had their own ‘national’ god, although there were a lot of gods in the general Semitic pantheon which they also recognized, and there was a pecking order in the divine realm as well - some gods are clearly recognized to be superior than others. Chemosh for example was the favorite god of the Moabites; the Edomites worshipped Qaus; the cities of Tyre and Sidon considered Melqart and Eshmun as their tutelary deities, respectively.
That being said, the whole concept is artificial in that no person in the ancient world would have used these labels and, as is often the case, a single religion might conform to more than one category (in other words, we can’t pigeonhole ANE religions neatly into clear-cut distinct groups). Take Egyptian religion for example: some scholars consider it to be generally polytheistic, while others argue that it also has kathenotheistic or henotheistic tendencies. Further complicating that is the high flexibility of it all: the tendency to syncretize and amalgamate different deities and the fact that Ancient Egyptian religion was not a monolithic institution, but a vast and varying set of beliefs and practices, linked by their common focus on the interaction between the world of humans and the world of the divine. (The same can be said of most ancient religion and mythology in general - be it Vedic, Greco-Roman, or Germanic paganism.)
People knew God at the time of Babel. At some point after Moses, the Egyptian culture completely forgot about Him. When did this happen? I can’t find anything in the Bible about it.