like an example
In Islam Christ is not considered the son of God.
Jesus is considered a Prophet of Allah. He's held in high regard but is not considered divine. He actually never died or was crucified, It only made to appear to be so. Allah sent down from heaven someone to look like him who was then killed. He's in The fifth heaven right now.
The implication of this is Allah who is all knowing, sent a doppelganger to die in the place of Jesus and in doing so deceived the world. because Allah who is all knowing would obviously understand that people who observe this crucifixion would then create a religion based on that perception of Jesus.
And whenever I then press the question okay if somebody's genuine belief in that religion is held does that person go to heaven or hell?
All of this occurred before the prophet Muhammad or The Quran was revealed. The church is older than the Quran and its institutions preceded it.
If those followers whose belief is genuine and they are then presented with the Quran and its truths but they reject it, because their belief which was established prior, How does God judge them when God deceived them into that false belief in the first place?