Can't help wonder how Noah got over 5 million different species on board the Ark. x2=10,000,000+ individuals. If you don't allow for evolution at least post-flood impossible!
Jesus specifically referred to various people as sheep, goats, donkeys, serpents, dogs, swine, foxes, wolves, worms, etc. as is consistent with a talking snake and the described wild beasts of the field in the OT.
If you consider that the animals brought 2 by 2 on board with Noah were of the human kind, there would have been no more than a couple dozen people.
As far as where did all the people go, genetic research suggests that about 75,000 years ago there was a cataclysmic event which reduced the human population from millions to a few thousand worldwide. Also a crater on the bottom of the Indian ocean suggests an impact event that would have instantaneously vaporized billions of metric tons of water into the atmosphere causing a worldwide deluge of super storms, tsunamis, etc which dates to the approximate time of the story of Gilgamesh which many believe the story of Noah was based on..