Archaeologist here: you’d want to really, really narrow down on what you mean here, otherwise we will clean your pockets pretty easily. Since about 2016, new discoveries of ancient civilizations, predating the most reasonable estimates crop up like mushrooms.
My estimate is that we will have several proofs pushing the the origins of civilization at least 10k years backwards, if not more, in the very near future, likely along the vectors of: - Gobeli Tepe and other Turkish/Anatolian ruins being significantly older than we thought. - The Sphinx and some of the Egyptian stuff being significantly older than we thought. - ruins in Indonesia that have a good chance to be proven older than all of the above. - Pacific Connection (Australian Aboriginal People and some Sth American tribes being related) being confirmed, thus pushing the colonization of America at least 12k years further back, via boat no less. - evidence that copper, iron and tin were smelted significantly earlier than we assumed.
In other words; current established estimate is that civilization as we know it is at best around 12k years old, and did not really kick off for real until 6k BCE. But we keep finding evidence that pushes that back at least to 25k BCE. We also keep finding evidence that both neanderthals and denisovians split much earlier than we thought, were much more numerous, and survived longer than assumed, so it is completely possible that there was a proto-civilisation 20k years before Sumer even existed, and that, conceivably, you could have Neanderthal humans witness it (or possibly participate?)
The explanation still has to ultimately relate back to explaining uap.