Our world have about 4,200 religions and beliefs, to research all their different holy books may consuming too many times or there's not enough of one's life time to research all of them.
Even when a person did research, assume he found the exclusivist religion A's God to be the true God, but other different exclusivist religion may still regards exclusivist religion A's God as false God.
If a person's conclusion is that he disbelieve in all religion's God and be a good person, exclusivist religion may still call the person sinner.
But this is just a statement without evidence to support it.
Or that this religion did provide some supernatural/spirituality evidence, but this supernatural/spirituality evidence cannot be objectively replicate to show to non-believer.
This supernatural/spirituality evidence can only be testimony by believer and it's accuracy is inconsistence.
Many other religion may also have this kinds of supernatural/spirituality evidence to support their religion's claims.
It's not non-believer's fault to disbelieve in those exclusivist religion if they feel the evidence is unconvincing.
The conclusion is everyone will only believe/follow what convince them. Maybe there've 1000000 versions of different interpretations of true religion/beliefs, everyone will still choose their preferences to follow with.
Do you agree with me that God sends prophets to people to convey His word ? Do you agree that God who deserved to be worshipped is just enough to not leave us without any guidance (books) in this messy world ?if the answer is yes then Pudding prophets of God are known not only to Islam but to Christianity and Judaism ... noone can deny that Abraham , Moses , Noah , Jacub , Joseph , John , David , Solimon ., Mohammed ...etc are all messengers from God all came with miracles to people as an evidence that they are sent by God .No one can deny that each messenger came with a book for example :Jesus with the Bible , Moses with Torah , David with the psalms , Muhammed with the Quran .....
Each prophet came in a certain era with a book from God as a guidance to humanity and all call to the same msg that God who deserves to be worshipped is the Creator , the Sustainer , the All knowing , the All hearing , the All seeing the Merciful and so on ...
Each prophet predicted the one coming after ...
For example , Moses predictef Jesus ...
Jesus predicted Muhammed ...
NOTE : all prophets support each other , they are not contraducting or fighting coz they all call for the same issue ...
That s why in Islam , it is a must to believe in all prophets and if one denies one of them he turns to be a desbeliever...even Jesus .. if a muslim denies Jesus , he turns to be a disbeliever by Islam ... in the Quran there is a whole chapter called "Mary"
What about other religions do they have messengers , do they have books from God .. may be you will tell me yeah they have holy books .. describing them as holy is as regards to them not to God ( the creator )