Salam
There are verses that show, those who truly believe in the next world, believe in the Quran. There are verses that show those who truly believe in God, will believe in God's Ayat and not disbelieve in them. And there are plenty of verses that show, those who truly believe in all of the book, will be guided by it to the straight path and it will become vividly clear to them, it's proofs and signs that it is.
These verses are understood, that if a person has the means to be guided and believes in God, God will guide his heart.
There are exceptions to the rule, those without power to believe or disbelieve, but keep in mind that even in that time, as hard as it was to travel, the Quran showed if they can travel, they had to search out God's Messengers on earth and come to God and his Messenger. The fact, if they were traveling and searching and never found it and death came to them, they get rewarded by God.
In this day and age, it just takes a little time off your day to research what the sent ones by God have brought to humanity and research their words a long with reflecting over holy books and researching religion, is not the daunting task it was in the past.
It's MUCH EASIER to research religions right now and even be aware of the disputes and differences and build methodology of knowing what is true and what is false.
There are people without even access to clear water, let alone means to know religions out there, let alone see past the darkness of Islam as is, and see what Islam was meant to be, in this day and age. These people are the exception, they can be of any religion and God will mostly likely forgive them, as long as they don't murder etc, you know what I mean.
There also a case of a certain people who are neither good or evil, but are living in a place where their affair is totally in God's hand and no one knows their fate, not even the witness of our time, who sees their deeds, but rather, their inner secret despite his witnessing deeds in unseen forms - they are still so hidden, not even the Imam (a) of our time knows their fate. The thing with these people, if the trials don't make them shift one or the other in this world, it is said, there will be trials for them on the day of judgment and so their test is not done even the life after death doesn't complete their trial.
This is where people are exception to the rule.
Another thing to mention is there levels of hell. Stubborn denial or hypocrites of Muslims who have proofs but don't apply their knowledge, is the lowest fire gate way.
But among the gateways although much less evil, is choosing never to give the ones sent by God a chance to guide you, and never giving Gods' book a chance to guide you, not giving God's rope a chance to help you, but just ignoring or denying it while not knowing.
This is a much lower evil, these type of people can be easily saved, if people go out to them and teach them or they witness miracles, so it's really sad, that we don't try to guide humans in general and push them to seek knowledge.
There are levels of hell compared to other levels seem like those people are not evil compared to the more lower gates, but still, they are ALL evil though their evil status significantly is different, that if you were to compare them, one appears almost like saints compared to the others.
At the end, the way to paradise, and it won't be accepted otherwise, with some exceptions only (without means to know the truth), is really through sincere love of God that you value nothing else on par with that Great being and that you believe in his Wrath, that you actually do fear him and don't feel safe from his displeasure.
If we are free of Shirk we enter paradise, and while our minds can be convinced there is only one God, it's the heart that has to be trained to value God above all other things and people and the dunya has to be so low in our eyes, in fact, hated to a degree because it leads away from God, it's this SHIRK that is harder to defeat.
We have to also love God to the extent that we only attribute him truth that we know and have proof for, and not attribute him through ignorance or trusting others to attribute God on their claim they study his religion and know how to teach his teachings when they don't present proof and mixed falsehood with truth and mix fame and money with religion and have made their career path and confirming forefathers concerning religion interwined.
God requires sincerity that we do value him and love him above all else. If we do, we enter paradise. So oneness of God is enough, but the Quran shows, those who do unify him will come to the proper guidance of God and be acknowledge the current guides or rope or family of the reminder or reminder.