Well, it was never going to look like the Americas even if it was true. The claim is that they discovered the land, not that they circumnavigated it or were able to chart the coasts with Renaissance-level precision.
There’s no good or compelling evidence. But there’s lots of ‘evidence’ that while dismissed by most academics, can be used in support of the theory in a vacuum, for example the existence of a pre-Colombian carving in Arabic (which isn’t actually that, but was believed to be by some).
The idea isn’t based on the map alone, it’s only one piece of the corroborating ‘evidence’.
Again, I’m not arguing that it’s a true claim, just that it’s not on the surface insane