Who was crucified instead of Jesus (peace be upon him) and where is his grave? Why has Allah led the Christians astray throughout history? And does Allah increase the wrongdoers in their straying?

There is no benefit in knowing the person who was crucified instead of Jesus (peace be upon him), nor his grave. Guidance from Allah is a divine bestowal of faith and righteous deeds, and it is only attained by those who are worthy of it. Allah knows best who deserves guidance and guides them, as He (the Most High) said: "Indeed, you do not guide whom you like, but Allah guides whom He wills. And He is most knowing of the [rightly] guided." Their misguidance occurs due to their injustice, as He (the Most High) said: "And Allah sends astray the wrongdoers. And Allah does what He wills."