The Black Sea Deluge Hypothesis posits that around 7,500 years ago, the Mediterranean Sea breached the Bosporus Strait, causing a massive influx of water into the Black Sea. This event transformed the Black Sea from a freshwater lake into a saltwater sea, resulting in a dramatic rise in water levels. This rapid flooding would have submerged large areas of land, displacing human settlements along the coastline. The catastrophic nature of this event is believed to have been preserved in the oral traditions of ancient cultures, leading to the creation of flood myths, such as those in the Bible and the Mesopotamian epics like the Epic of Gilgamesh. Archaeological evidence, including submerged prehistoric settlements and shifts in the Black Sea's shoreline, supports the idea of this sudden and profound flooding event. The Black Sea Deluge is considered a key historical event that likely influenced the development of various ancient flood myths across the Near East and beyond.

"most people mean"

implies most people since the King James version was published. Not at all clear that's what author meant; the concept of the world as we now know it didn't exist then.

So very reasonable to conclude that the Great Flood in Genesis was meant to describe a regional megaflood, which innundated the "whole world" meaning all of Mesopotamian civilization.

And there is archeological evidence of ancient cities totally buried in mud, i.e. as you say regional megafloods.

I don't think that's true at all. The narrative is very clear that all humans and land animals that are not on the ark die, and in the Talmud I'm not aware of any debate that all humans died.