I view Moses as a character similar to King Arthur. We can be pretty sure that there wasn’t really a King Arthur who was conceived when a spell of Merlin made Uther Pendragon look like Gorlois and thus let him mount Igraine and we can be pretty sure there was no round table and love triangle with Lancelot and Guinevere. At the same point there is a human gravity-well that exists ca. 500 that implies there was a great warlord at that time: Anglo-Saxon invasions stopped or at least greatly slowed down for a generation, tales of a great warlord exist from chroniclers and writers who would have existed in living memory of Arthur:
St. Gildas is one who could and probably did interact with the historical Arthur and wrote a screed about how the British (as opposed to the English) ultimately lost out to the Anglo-Saxons because of their sins. He mentioned a great British warrior (one he has little respect for as a person but concedes was all-that on the battlefield) who stemmed the tides of invasion for years but was not a Christian (one more piece of evidence for divine wrath against the Brits) and while he never names him he does refer to another warleader as having been a “horse warrior and charioteer for The Bear”. Gildas, writing in Latin, used Ursus, but in Celtic dialects bear is Arto, or, Arthur.
In the poem Gododdin written about 600 there is a line about a great warrior of the late 6th century of whom the writer says
implying the name Arthur was already associated with military greatness. Nennius writing in the 9th century from no longer extant sources makes reference to Arthur as well, again showing that he was clearly known and remembered by this time.
So there probably was a real Arthur who may or may not have been a king in title but had the power of one and who whipped some serious Anglo-Saxon ass in the early 6th century, enough that the combination of military defeat and treaty returned some conquered territories and stopped the invasions until after he was dead and then some (when the Anglo-Saxons came back and completed the conquest). He was probably a Romano-Celtic pagan rather than a devout Christian, which explains why Gildas did not name him (plus he was probably borrowing from some Roman historians who also did not give the personal names of people they didn’t like), plus Gildas wasn’t writing history so much as an indictment of the sinful British. Variants of the name Guinevere even appeared fairly early in the legends so it could have been he was married to a woman by this name or something like it, though the name Lancelot did not enter until centuries later. (Bedivere, by a variety of spellings, is the oldest knight associated with him, mentioned in Gildas.)
The Middle Ages took the existing legends and twisted them like a monkey on acid handling a ball of Play Dough. They took other already existing legends and merged them, as well as probably taking some actual history that survived (such as the invasion of Europe by the British warlord Riothamus) and tacked it onto Arthur. They fleshed out Arthur and Guinevere and gave them some nice tragedy, they tacked on all manner of other tall tales and legends and above all else they gave the tales an overarching moral of chivalry and honor and ultimate downfall. What exists has only a kernel of the original legend but the name survived and the great battles and military prowess.
With Moses I think it was probably something a bit similar: a clan leader of a semitic group who left Egypt for Canaan, possibly inspired by the short lived monotheistic reforms of Akhenaton, and encountering some opposition from royal forces and some major internal conflict twixt monotheists and polytheists, then entering Canaan and taking territory through a combination of military conquest and intermarriage and treaty. Mosa is the Egyptian suffix for ‘son-of’ and could have been part of a name or part of a title- names and titles often get merged (Sallah al dinh Yusuf bin Ayyub becomes Saladin, Kerl becomes Carolus Magnus becomes Charles le Magne becomes Charlemagne, etc.). I don’t believe he parted seas or received tablets from heaven or that the exodus he led was hundreds of thousands of people, but I would be more surprised to learn there was no basis at all for the exodus story than that there was; among other things I doubt the legends would have had the staying power if there was no historical touchstone (places, bloodlines, relics) to connect them to as while it’s easy to embellish the facts it’s difficult to make up a group’s history out of whole cloth and get away with it.