What are the non-scriptural evidence (if any) on biblical Joseph story, where he becomes Grand Vizier of Pharaonic Egypt in 15th century BCE. I know that the pharaoh is unnamed, and the era is close to the second intermediate period which was chaotic and lacking of official documentation.
If there is no evidence whatsoever, can this story be called a legend and in fact false ? From a historical point of view.
First: A warning. What you're going to get on this website is going to be the fruits of the Documentary Hypothesis and similar historical approaches. This often clashes with some folks' "fixed beliefs". I'm a Christian myself, and have no issue reconciling my faith with secular scholarship, but some faith traditions have big problems with it.
The first thing I need to lay out here is that the text of The Torah was never intended to be a literal history, but rather a religious document. It was crafted and honed over the centuries with the purpose of furthering the faith of the Jewish people, not out of any modern scientific sense of devotion to Historical Accuracy. So to look to call stories in The Torah "false" (or "true"), is completely wrong-headed. There are some historical nuggets we can sometimes glean from them, but they were not written by or for historians.
This goes particularly for anything in Genesis (including the story of Joseph). The current scholarship is that no part of it was written down prior to the Babylonian Exile (6th Century), which is by most folks' reckoning thousands of years after the events described. The Joseph story in particular was written down no earlier than the 5th Century BC. Genesis is almost universally accepted to be a collection of Jewish myths and folk tales, so demanding historicity out of it is no more sensible than looking for the birthplace of Babe the Blue Ox.
To take another example, Exodus was likely an allegory, composed while the Jewish people were enslaved in Babylon. Does that make it "false"? Tell that to the oppressed people the world over who have used that narrative to help gain their own freedom ever since. Is the story of The Battle of Jericho "false"? Tell that to the slave who sang Joshua Fit The Battle to remind his masters what God's wrath looks like, then lived to see Sherman's army burn that plantation to the ground. There's truth, and then there's Truth.
The whole story is mythical in nature and intention. Even finding similarities to actual events is seen as quite the fruitless endeavour.
The biggest problem with this question is that it asks for the historical validity of the Joseph-story in its biblical version.
But while the story is set in the second millennium BCE, it was first written down in the first millennium BCE (~400 BCE*). That is 1000 years after the events described are said to have been happened.
But the problems do not stop there.
The Bible was not set in stone, the Tora was not set in stone. But constantly written and re-written for a long time. We currently do not know exactly when the texts really solidified, but it was much later than the Babylonian exile.
That means that the current biblical text as published in books called "Bible" today is far removed from the text as it was written down first. Looking for any historical evidence in that book is hampered by later additions from the biblical editors. So much was added that the text as such is almost unreadable now.
Luckily, historical critical scholarship has attempted and is constantly attempting to unearth the original story, the urtext. The most crucial work in this field was presented in 1991 by Harald Schweizer.
While mainly in German the following book is continually updated and also contains an English translation of what his team now believes to be the original Joseph story.
Harald Schweizer: "Josephsgeschichte", Tübingen, 2. Oktober 2017. (online, large version, 3971 pages, 21MB, PDF!))
Compared to the current version in most books sold today, you might compare the start of the story from page 1970 in that fantastic Schweizer book (actul translation by Jo Van Vliet):
JOSEPH was as a guardian together with his brothers at the small livestock. He was just a small boy. ISRAEL loved JOSEPH more than all his sons because a son of his old age he was to him. He had therefore made him a coat of many colors. JOSEPH once dreamed a dream, and he told his brothers, and said to them: »Hear, I pray you, this dream which I dreamed! There! We were binding sheaves in the middle of the field Suddenly stood up my sheaf, and even stayed upright. And, there round about stood your sheaves, and bowed to my sheaf. There his brothers said to him: »You want to be a king someday, king of us? Or reign, you want to reign over us?« And jealous of him were his brothers. Whereas his father retained the incident. JOSEPH’s brothers went to graze the small livestock of their father in SHECHEM. And said ISRAEL to JOSEPH: »Are not your brothers presently as shepherds in SHECHEM? Then go! I want to send you to them.« He said to him: »I am ready.« And he said to him: »Go then! Ascertain the well-being of your brothers and the well-being of the flocks, and bring me word again!« And he sent him out of the plain of HEBRON, and he reached SHECHEM. Ran into him a man as he was wandering around the open field.
Also note the quite positive mental picture that emerges of "Egypt" from a Hebrew perspective. This is in the starkest and unexplained contrast to the following Exodus narrative where Egypt is a slave-driving hell on earth. The whole story is so generic in its corner points that actual historical hints are really not found at all.
That said, some kind of historical motive in the Joseph story might be found in the actual history of King Jeroboam who fled to Egypt and was treated well there. But while the book of Kings is somewhat on firmer historical grounds, that story is shrouded in mist as well and only ever so slightly better as a historical source. Going by the archaeological evidence, even that king never existed in any form near what is written down about him in our texts. But note how the traditional dating of Joseph clashes with Jeroboam –– or gives hints towards the improbable historicity of Joseph.
*: Or even later, for the original, first version, during firmly hellenistic times around 300BCE. A: Kunz: "Ägypten in der Perspektive Israels am Beispiel der Josephsgeschichte", BZ 47, 2003, 206–229.
And a seriously considered dating, albeit on the outer side of extreme, 100 BCE: B.J. Diebner: "Le roman de Joseph, ou Israël en Egypte. Un midrash post-exilique de la Tora", in: O. Abel & F. Smyth (Eds): "Le livre de traverse de l'exégèse biblique à l'anthropologie.", 1992, 55-71.
Konrad Schmid: "Die Josephsgeschichte im Pentateuch", in: J.C. Gertz & K. Schmid & M. Witte (Eds.): "Abschied vom Jahwisten" (BZAW 315), deGruyter: Berlin, New York, 2002, 83–118:
The Joseph narratives (Gen 37-50) are a testing ground for every hypothesis on the Yahwist as they serve as the transition from the book of Genesis to the book of Exodus in the final text of the Bible. It is clear that these narratives were not created for this purpose, but were rather modified for this purpose in the course of their literary history. The Joseph cycle seems to connect primarily to Gen 12-36. It was expanded later as a bridge to the events narrated in Exodus. The most recent discussion has raised the questions whether it ever existed independently of Gen 12-36, whether it ended originally in Gen 45, or whether the entire cycle must be dated after P. This study aims to show that it remains plausible to assume an independent, pre-priestly Joseph-narrative as contained in Gen *37-50. This original narrative was created as a critical response to Ex(ff.), especially to Sam, and connected to the book of Exodus after P.
It is a matter of belief. History after so many milleniums is completely open to interpretation. If someone says something is found and the adherents believe it, then it is true.
It is called Faith.
https://en.wikipedia.org/wiki/Siege_of_Antioch
During the siege of Antioch, the desperate crusaders facing impossible odds found a lance their priest said was the holy lance.
The knights of christiandom believed it was the true lance. Morale surged. And the Christians won.
The point is history and relics and facts are all interpreted. No one believed any historical provenance was traced, any forensic tests were done, or any DNA sample was taken.
But the crusaders believed, and they won.
If you want to believe Joseph story was valid you will find historians to support you.
If you don't want to believe, you will also find that.
Religion is myths.
And its power lies in people believing it.
