The story of Atlantis appears in Plato’s Timaeus-Critias (c. 355 BCE) as an oral tradition Solon acquired in Egypt and adapted into an epic poem, but which he left unfinished. Nevertheless, Solon told the story to his family relative Dropides, who passed it orally to his son (Critias the elder), who in turn told it to his grandson (Critias the younger). Either this oral transmission actually took place, or Plato was the fabricator. If the latter, the entire tradition (including the island of Atlantis) is likely to be fiction. This article shows there is a lack of evidence for the Atlantis story being an authentic oral tradition and highlights problems with the transmission. Supposing oral retellings of the tradition did take place, it is seemingly impossible to distinguish fact from fiction in the story since the tale of Atlantis must have been garbled as it was retold over generations; reciting a tradition by word of mouth is unreliable.
Smith, O. D. (2016). "The Atlantis Story: An Authentic Oral Tradition?". Shima: The International Journal of Research into Island Cultures. 10(2): 10-17. Link/PDF
Note: I thank Philip Hayward (Shima editor) for his peer-review feedback.