just floods in general.
Yes I think this is correct.
Plato places this back 9,000 years from his day. Most civilizations were still using very natural materials, and the larger and more advanced of these lived near the coast. Given that a lot of ice was still melting in the north and sea levels were rising, it seems very possible that most early civilizations during that time were built on coasts that are now far under the sea.
Plato says the Egyptians mentioned a large power in the west that held most of North Africa up to Egypt's borders, parts of Spain, and the bottom half of Italy (as well as islands in the Atlantic)—but the people in what is now Athens fought them back from further advancing east.
Not that a specific event is recorded, but in general, this sounds possible and like the exact type of general activity that would be "big news" in the Mediterranean 11,000 years ago.
I think this is something Plato probably believed to be true—he would have wanted it to be true. As he says, it shows that Athens was, in a way, destined to be great because of its geography and because of the race of those who live there. Solon, a relative of Plato and the origin of this story, famously did travel to Egypt and was friendly with their government.