"There were advanced civilizations that got destroyed 12000 years ago" isn't an archaeologically or scientifically grounded statement. It's magical thinking based on no evidence.

So scientists generally don't address it, just as they don't address dowsing or necromancy, except insofar as these beliefs are part of culture.

Sounds like conspiracy stuff, yet I can't find anything about it except niche sources with info that seems to agree with it.

Well there you go. The only sources you can find that discuss this are, to your own eye, "niche sources".

Working archaeologists and anthropologists don't spend a lot of time holding conferences to demonstrate that leprechauns don't exist; no one writes a paper "Metaanalysis of end-of-the-rainbow excavations finds no 'pot of gold"

Followup question -

Per my recollection of the consensus a few decades ago when I was in a school, 'civilization' started up independently at about the same time ~5000 years ago, IIRC in Egypt, Mesopotamia, the Indus Valley, and the Yellow River in China (maybe a little later, but with disputed evidence of it also being earlier.)

What was so awesome about 5000 years ago that was not present 12000 or 50000 years ago?