Fiction, myth, legend, or fact, I don't really care if people search for it and otherwise completely agree with your concluding points. I lean towards it or something like that described in the myths and legends did exist. I know you believe in the Shift. The Shift story includes the Fall. https://jodieshelm.medium.com/what-caused-the-earth-to-fall-in-the-first-place-889402f1c77f

I assume that whenever that happened, an Atlantean type civilization was around then.