Come, let us reason together.
A world exists external to you. You know about it through your senses. It can be called 'nature' or 'objective reality' (&c).
Out there is what scientists, and archaeologists, and many other thoughtful people study in order to understand what reality is.
Accurate statements about that world are called 'true'. This means that if you want to know whether a given proposition about reality is true or not, you can check reality and see what answer you find there.
Thus we find in the bible a description of the "Genesis flood". In that report all living land things except a single boatload died by drowning.
If the story is true then there will be real evidence of it out there. We can roughly date the story by working out when and where woodworking technology might make the building of the ark possible. We can very generously allow it would have to have happened in the last 7,000 years.
Such a worldwide flood would necessarily leave a geological flood layer all over all continents and islands and the sea floor and that layer would necessarily be no more than 7,000 years old. Is there such a layer? No, there isn't. Is there anything resembling it? No, there isn't.
In the story, the flood covered the tops of the tallest mountains something like 20 feet / 6 m deep. The tallest mountain 7,000 years ago was Mount Everest. Today its top is 29,029 ft / 8,848 m above mean sea level. The Himalayas rise at a steady but very small rate due to tectonic pressure, so let's say 7,000 years ago Everest was only 28, 870 feet / 8,800 m high. How much more water than presently exists on earth would be necessary to cover the top of Everest 20 feet deep? Answer: more than 1.1 billion cubic miles. Question: where is that water now?
In the story, Noah took one, two or seven breeding pairs of each animal species aboard the ark. That means that all living land species are descended from a very small breeding group that existed no more than 7,000 years ago. If it happened, such an event can be detected in the genes of modern animals (called, amongst other things, a "genetic bottleneck"). And if it happened, such a genetic bottleneck, pointing to that date, will be found in the genes of all modern land species. Do we find such genetic bottlenecks in all land species? No. A few land species? No. We don't find it.
So from the evidence of reality we can conclude the story is not factual.
We can also trace the story back to Sumer, in Mesopotamia, It existed, at the least, around 2,500 BCE, which as you know is about 1,000 years before the bible God appears in any records. The Semitic Akkadians acquired it, and it became a story known in the Babylonian world, and you may recall that Abraham was said to be from Ur, a Sumerian city with a substantial Akkadian population. In that story it was the Sumerian gods who sent the Flood.
So from the evidence of history we can again conclude that the story is not factual. However, we might also be tempted to hypothesize that it had its origins in a very substantial flood on the Tigris or the Euphrates at some time in the far past. (The earliest evidence of the Sumerians in Mesopotamia puts them there by 5,000 BCE.)
Reality is useful like that. It can give you insights into what's true and what's not.
