I have a hard time believing that either the Greeks or Egyptians would get that wrong
when they mentioned it so many times during Timaeus and Critias.
Well, the reason for this is surely that you are not familiar with the usual mistakes common in all the ancient literature.
The existence of boats and settlement does not mean that there is knowledge about these countries.
The known geographical horizon widened slowly step by step ... very slowly.
And this is not a guess, this is academically supported fact.
One of the basic mistakes of most (not all) Atlantis searchers is that they concentrate on the Atlantis story,
but do not see Plato's whole work, not the works of other Greeks, not the works of other non-Greek authors.
The picture becomes much richer by this and many strange things in Plato's dialogues become much clearer.
Atlantis in the Atlantic? I do not have a hard time to believe this - because I know there is no chance for this.
Not at all. Not geologically, not philologically.
But may everybody believe what he likes to believe.