Advanced ancient civilizations theory - as in, there were technologically complex civilizations in the paleolithic long before the neolithic period (when we usually say they emerged). I don't think there's any evidence for this, and its main proponents are people like Graham Hancock who is not a serious scholar in any way. Even then, it's a difficult question to answer. Though, not an impossible one and I've talked about the issue in this post why we know there aren't "lost civilizations." Tldr, it's incredibly unlikely that we'll find another Mesopotamia 20k years ago, but not too unlikely that we'll find another small community of well-organized foragers like at Gobekli Tepe. This raises another question, it seems strange that humans only created "civilization" so very recently when we had so much time to do it. I've talked about this in this post why didn't people create civilization earlier? And tldr, humans intentionally lived in ways which minimized our impact on the local environment, living so that our lives (and our buildings) fit into the cyclical and impermanent powers of the world. When the "neolithic revolution" happened, what actually changed was the ideology of societies: it became acceptable to disrupt the local environment. If you're wondering exactly why Graham Hancock's argument is false, see this review of his most recent book by Jason Colavito.