Islam denies the crucifixion.
That is like a history revisionist denying the World Wars, moon landing or the sinking of the Titanic.
There were various Authors that did not directly contribute to the NT. Perhaps early Muslims read the work of the wrong Author. Remember, a lot of this was happening before the Black Plague and Dark Ages. Much was lost. For me lots of what the Monks of the Catholic church carried forward is debatable. Look at the work of Martin Luther and the carnage that followed after him. I believe that the KJV did a lot to order the Christian Church after. It was fairly recently that a Catholic Pope told Catholics to read their Bibles.
The Crucifixion happened very early, and the founding of Islam would not happen until around the 7th century. And, of course Islam split into Sunni and Shia branches, and finding out about that did a lot to undermine the credibility of Islam for me. Even Sunni Islam has 5 branches. I wish people could just get along.