From
https://islamqa.info/en/answers/22029/
"3 – The difference between this righteous slave, and the Macedonian Alexander who was a kaafir, is well known to Muslim scholars. Ibn Katheer (may Allaah have mercy on him) said in al-Badaayah wa’l-Nahaayah (1/493):
“It was narrated that Qutaadah said: Alexander was Dhu’l-Qarnayn and his father was the first of the Caesars, and he was one of the descendants of Saam ibn Nooh (Shem the son of Noah). As for Dhu’l-Qarnayn, he was Alexander son of Philip… ibn Roomi ibn al-Asfar ibn Yaqaz ibn al-‘Ees ibn Ishaaq ibn Ibraaheem al-Khaleel. This is the genealogy of him given by al-Haafiz ibn ‘Asaakir in his Taareekh. (He is known as) the Macedonian, the Greek, the Egyptian, builder of Alexandria, on the events of whose life the Greeks based their calendar. He came much later than the first Alexander. This was approximately three hundred years before the Messiah. The philosopher Aristotle was his minister and he is the one who killed Daar ibn Daar (Darius) and humiliated the kings of Persia and invaded their land.
We have drawn attention to him because many people think that they are one and the same and that the one who is mentioned in the Qur’aan is the one whose minister was Aristotle, which has resulted in a lot of mistakes and far-reaching corruption. The former was a righteous believing slave and a just king, and the latter was a mushrik and his minister was a philosopher. There were more than two thousand years between the two, so what comparison can there be between them? They are not alike at all and they have nothing in common, except in the mind of a fool who does not know anything.”
4 – The Christians have no information in their holy book about the second Alexander, let alone the first. All they have is the story of the visions of Daniel, which they claim refer to the rule of this infidel Alexander, and the division of his kingdom after his death.
5 – If we assume that there is a difference between what the Qur’aan says and what their book says about a person or an event, why should that be regarded as strange? There are many such differences, especially in the stories of the Prophets such as Ibraaheem (Abraham), Nooh (Noah), Loot (Lot), Moosa (Moses), Dawood (David) and ‘Eesa (Jesus) (peace be upon them). The Christians have no reliable and continuous chain of narration for this book in which they believe, and they know nothing about those who translated it. Moreover it contains dozens of contradictions which effectively nullify any claim to infallibility or to have been written with inspiration from the Holy Spirit. It is sufficient to note the contradictions in the genealogy of Jesus (peace be upon him)!
So how can we take what is in these distorted books as a standard by which to judge the Holy Qur’aan which is preserved by Allaah?!"