It all has to be magic. Case closed. Shut up and believe. You can if you try hard enough. Just like IDK could believe Hinduism or Scientology or Rastafarianism if he tried hard enough.
Honestly, if there had been a massive global flood with the extinction of all air-breathing organisms at any time in earth's history, it would be the first thing every biology and geology student learned, starting with the first day of class. Week one would be "The Flood and how it shaped our earth". The rest of the term would be spent examining all the thousands of pieces of evidence.
We know what floods look like and what they leave behind. There would be no way to miss the evidence. It would be all over the place. Nobody would have any doubt. How come university departments don't do this? How come I never learned about any of the massive amounts of flood evidence in any class I ever took?
Why do all the facts-- DNA, fossils, glaciers, existence of civilizations that never noticed the global flood, geology, botany, palentology, biogeography-- tell an entirely different story from what it says in the bible? Why did god hide all the evidence of the global flood? It's like he wants us to believe just any old thing.
Noah made the ark enormous and really tight to keep all the flood water out. It was basically a wooden submarine. But we are not supposed to ask how the animals and humans breathed in a box sealed up tight like that, with no power or ventilation system. Full of methane gas. And really dark, unless you wanted to light a fire and create a giant exploding floating methane bomb. It would have been a giant floating coffin in a few days.
We are not supposed to ask why people didn't keep making awesome boats made like that, if the ark worked so well. You would think that everyone would have just gotten together whipped up another ark. When floods came again, the people just died. I guess folks conveniently forgot how to build arks. Or they were too busy inventing new evil sins.
And we are not supposed to ask why the magic sin-removing flood did not even work as it was supposed to, since the evil snapped right back in place like yoga pants on a T-Rex. We would be willing to believe something like that had happened, if there was some physical sign that something like that had happened.