In this video, apologist Mike Winger looks at this question - about the fate of those who have never heard the Gospel:
https://www.youtube.com/watch?v=geMXJX3Q6sE
And in greater detail here: https://www.youtube.com/watch?v=IiyxpE5UBz4&t=0s
The realization that vast millions die without ever having heard the Gospel and Jesus could be headed for an eternity separated from God is deeply disturbing to many - both to non-Christians and Christians as well. But ONLY God truly knows how He will deal with any given individual or how He will respond to one who wants to know the truth about Him, but yet hasn't heard the Gospel. God is unlimited in how He might reach such people - even some perhaps at the cusp of death. However God works with such people, Scripture is clear that JESUS is the only path / doorway into Heaven! The Bible tells us that God SPECIFICALLY places people in time and geographical place - but that does NOT mean that He puts people in places and time that would in any way PREVENT them from knowing about Him, or eventually knowing about Jesus - as again, He is unlimited in how He decides to reach people around the world.
And, as God is ALL-knowing, He has ALWAYS intimately known the hearts and minds of all who would eventually listen to and embrace Him - as well as of those who He likewise always has known would NEVER embrace Him, that would only ever resist and reject Him - no matter WHAT details of Himself He shared or revealed to them. Clearly, God's COMPLETE knowledge of all hearts and minds plays into how He places people in time and place, when and where. A person God has always fully known would only ever have a permanently closed, hard heart and mind to Him would be no better off in eternity, whether born where Christian churches abound, or in some remote location without the Gospel. And, of course, people can and often do reject what they already CAN know about God (Romans 1) without ever knowing about Jesus - the Old Testament is full of such people. One does not need to know about Jesus to reject God. If they are determined to reject what God has ALREADY shown people about Himself (per nature, science, their conscience, etc.), then then they are likely to be just as resistant to Him if they knew even more, and about Jesus, the Gospel.
So how have people responded to what the Bible says they CAN know about God? And did they become determined to resist God to the point of deciding to believe whatever lies they desired to, convincing themselves into become immersed in atheism / agnosticism / deism / New Age / polytheism, or whatever false religion or cult? Do they want to know more about what God has ALREADY shown them, or do they run from even that, to the lies they'd rather adopt instead? Or do they permanently resist and reject God, maintain atheism, agnostic beliefs, or follow whatever false religion or cult instead? If one lies to themself long enough, the basic truths about God they once knew (perhaps as a child or young adult), will begin to evaporate in their mind, and they'll become convinced of the lies they rather believe instead. So an atheist, whom once knew basic things about God, has become convinced that He does not even exist. Some even know who Jesus is, believe WHO He is, but nonetheless have refused to commit / submit to Him as Lord - just another type of rejection of God (see Matthew 7:21) - with the commonality of all of these types of rejection being motivated by people desiring to stay their own, little god - as opposed to serving their Creator.
Romans 1:19 For what can be known about God is plain to them, because God has shown it to them. 20 For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. 21 For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened. 22 Claiming to be wise, they became fools, 23 and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things. 24 Therefore God gave them up in the lusts of their hearts to impurity, to the dishonoring of their bodies among themselves, 25 because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen.