By capitalizing Flood I meant the Biblical version. You need develop a hypothesis for each particular legend, and some of them might even be true - local ones, for example. 300 years ago, though, many people believed in the Biblical one, today they don’t because it has been falsified.
Catholics are an example of a religion which has adopted its cosmology to fit the facts. But we have to wonder how reliable their communication with God was given that God gave them so much bogus information. And some historical events are at the core of Christianity, such as Adam and Eve and original sin. I’m sure you’ve seen the explanation of how original sin was a human choice without Eden, which I’ve found so convoluted to make the typical Nixonian evasion seem straightforward.
I’m Jewish, and in my education Adam and Eve were not that important, and not part of “real” history. However real history included the Exodus, so we’re no better off.
Well, we do have the Black Sea Deluge event. The flooding of what is now the Black Sea but which was probably the area where agriculture started. It happened about 5600 BC and might be what caused the spread of agriculture into Europe.
Though unlikely, due to the time span involved, it just might be the small kernel at the base of the Flood story.
A long time back someone on talk.origins posted a big batch - dozens - of flood stories from around the world, and they were fascinating to read. Some involved boats, some involved rafts, some, like the Greek flood story, involved mountains. Several had the heroes being the last people left - but when the flood dried up others walked over the mountains to see them. Nearly every place by a river (ie every place man lived) had floods, so it is impossible to tell whether a real big one or a relatively small one was the source of the legend. It is interesting that I am unaware of a flood legend like this from Egypt, but they understood their floods better than most.