There are plenty of things from the past that are absolutely real. We have tons of physical evidence for settlements all over the world throughout history. I’m sure there’s more yet to be discovered. But until we discover it, it’s just hearsay.
There may well have been a real place that inspired Plato’s mention if Atlantis, but only one. Not the many hundreds of possible locations suggested over the centuries. They can’t all be Atlantis, if any of them are.
Do you expect all the physical evidence of Elephants, such as bones, tusks, genetic samples, stuffed animals, photos and peer reviewed zoological descriptions, to disappear in the next 200 years? If so why? The Dodo went extinct 340 years ago and nobody thinks they were mythical. The mammoth even before that. Even dinosaurs are known to have existed, as a fact. We have vast amounts of physical evidence. So I really don’t understand what point you’re trying to make.
Perhaps he means non academic discussions like whether vaccines actually work that you find on forums. There's loads of people doubting established facts.
Moon landing denialism is a prevalent minority belief. I think it's within the realm of possibility that the Apollo landings may one day be regarded as myth by the majority, if society (once again) takes an anti-intellectual turn. The cynical dismissal of "Hollywood faked it because of the Cold War" is a very neat and tidy meme that spreads well as it is.
There may well have been a real place that inspired Plato’s mention if Atlantis, but only one. Not the many hundreds of possible locations suggested over the centuries. They can’t all be Atlantis, if any of them are.