How will God punish the disbelievers who did not convert to Islam even though they heard about it, considering themselves to be in the right just as Muslims consider themselves to be in the right?

This problem is an illusion; the proofs of Islam's authenticity are definitive. The Holy Quran is an undeniable argument for Islam's truth, unlike other books that have been subjected to alterations and falsehoods. The punishment of non-Muslims does not occur except after the prophetic message has been established against them, in accordance with His, the Almighty's, saying: "And We would not punish until We had sent a messenger" (Quran 17:15). This message is established by conveying the call of Islam to them in a way they understand.