Yeah I watched this video a while back when I initally discovered this topic but I rewatched it right now just to remember the main argument. His argument is essentially the Quran cannot be drawing from the Syriac Alexander story is because it dates to after the Surah was revealed.
But it fails to address the other older versions like Josephus’, which already contain the wall, Alexander travelling to the place where the sun sets, the mountain and the barbaric tribes needing to be contained.
It also doesn’t make sense historically if the Syriac copied the Quran.
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The original Syriac story was a Christian propaganda piece to help Heraclius in the war effort going on at the time. Also, in the video it assumes this story was unknown before the Surah which is false since the story was orally transmitted throughout the region. The whole point of the Surah being revealed was to retell the story, so it was obviously well-known to the Pagan Arabs and Jews.