Cadiz is an ancient Phoenician city, and the Phoenicians often built fortresses offshore from their main town, on a small island or rock, so they could just withdraw there when an army came by and they would be nearly impregnable.
So perhaps that’s what the divers found.
Alexander has entered the chat...
That makes far more sense than it being s mythical place that has likely already been found elsewhere, and is still being studied now. There are archaeologists who believe the story of Atlantis was based on the volcanic demise of Santorini/Thera-home of the Minoan civilization-in 1600 BC-there are plenty of Greek stories about the Minoans being advanced people who were also considered sinful/bad by their neighbors-the historical and archaeological record-and recent findings-put it a lot closer to being Atlantis than one of the sunken ports off the cast of of Spain-and as you pointed out-most of those belonged to the Phoenicians anyway...
Plato was not exactly an explorer who based his historical knowledge on actual knowledge of the facts-and he wasn’t born until after 300 BC in any case-a long time after Atlantis supposedly existed-but he did make a good cautionary tale about it...