Truthfully, the change that Akhenaten made to Egypt's religion didn't actually make it monotheistic, in a technical sense. The royal family (not just Akhenaten, but his wife Nefertiti, even the children) were promoted to gods during life (rather than only upon death, as with previous Egyptian kings - and only kings) - a trend begun by Akhenaten's father (though his father never included his wife and children in this). The royal family became the intermediaries between the people and the sun disk - the Aten, which Akhenaten promoted to prominence, and scrapped the rest of the pantheon. And I say intermediaries in the sense that the people were supposed to worship the royal family directly, as gods in their own right, and the royal family would in turn worship the Aten on behalf of the people. But the Aten was not the only god in his pantheon, since it included Akhenaten himself and the royal family, as living gods on earth. Even during the 17/18 or so years that Amarna was active as a city, and Akhenaten was in power, the people of Egypt didn't fully buy into his change. Excavations of the houses of Amarna (which was a city that Akhenaten built on virgin ground to get away from the religious power of Thebes) have turned up figurines of the traditional Egyptian gods that the people were worshipping in the privacy of their homes. So I don't think it would have come from there.

Edit: a source Akhenaten and the Religion of Light

It would be hard to pin down Judaic monotheism to one source or even influences from one culture. A few of the religions around the Mediterranean seemed to follow a Polytheistic to Henotheistic (or Monolatrism) to Monotheistic path (can be argued for the popular Egyptian and Greek religions especially). But while there are similarities in their religious practices and canons and given the unreliability and bias of the sources, it is hard to find a consensus on which culture or religion had the greatest affect on Judaism. Popular candidates include Zoroastrianism, the Canaanite religions, and the Greek religions for who had the most influence.

I don't know the answer to this question, but you may want to try r/BiblicalArchaeology/

A related question: Why did monotheistic religions come to dominate the world when historically it seems like most religions were polytheistic?

Is the idea that monotheism just makes more sense at all legitimate, or is that just blatantly western and Eurocentric?

I seem to remember Toynbee theorizing that the rise of monotheism was inevitable once the mass of the people reached a level of "sophistication" where polytheism was just no longer possible to accept.