Quite possibly some truth, some fiction. New findings with modern technology uncovering many ancient buildings, structures, temples, etc., are happening more and more frequently. There could very well be an ancient place that sunk thousands of years ago that was advanced for the time, just as well Plato’s story could be pure fiction. Neither one has been proven. Yet.
Zero possibility of any truth. ALL FICTION.
Could there be lost cities? Of course. But NONE of them are Atlantis. Atlantis is fiction. Pure 100% fiction. All the way through.