Even if the flooding was thousands of years earlier, there would likely be some oral history of its occurrence. How that might change with time is up for debate.
Yes but even myth often has some basis in fact. It’s amazing how many stories from the Bible and elsewhere that were once thought of as mere myth have been found to be true. The Trojan War was once thought just literary fantasy. The Hittites were once considered a Biblical myth, but now we know there were a major civilization before the Bronze Age Collapse. We still have a lot to discover about the ancient past, and a lot that will probably remain hidden forever.