Why is the story of Dhul Qarnayn so similar to Syriac Alexandar legend?

The story of Dhul Qarnayn in Sura Kahf is very similar to the Syriac Alexandar legend , including key narratives like travelling to the setting and rising places of sun and sealing of the Gog and Magog using a barrier which is prophesized to break in the future. Muslim scholars mostly seem to agree that Alexandar couldn't be Dhul Qarnayn since historically Alexandar was a polytheist while Dhul Qarnayn is a firm believer. The bigger problem is historians unanimously agree that this legend is just that, a legend, and doesn't have any historical basis. Moreover, the prominent hypothesis is that this story was created as propaganda and the prophecies are ex-eventu. Why would Quran's narration shares so much similarity with a legend that has very questionable origins? And does the Quran's narration meant to be taken as literal history or is it possible to interpret it as an allegorical story? **References** There has been many papers written by secular academics on this topic. Some notable ones - - Kevin van Bladel, “The Alexander Legend in the Qur’an 18:83-102,” in The Qur'an in Its Historical Context (2008), edited by Gabriel Said Reynolds - Tommaso Tesei, The Syriac Legend of Alexander's Gate: Apocalypticism at the Crossroads of Byzantium and Iran (2023) - Stephen Shoemaker, The Apocalypse of Empire, University of Pennsylvania Press 2018, pp. 79-86. - Marianna Klar, "Qur'anic Exempla and Late Antique Narratives," in Oxford Handbook of Quranic Studies, Oxford University Press, 2020.