All evidence at this time points that agriculture based city states were challenging to boot into a "proper civilization". If you raised taxes, your citizens would just leave since the area you could control was quite small. And then you get new diseases that suddenly could spread dense in urban population - wars - all that good stuff.
Based on the book, maintaining a city state over more than few generations, before the knowledge how to keep it going has been learned, is really, really really hard.
This is not to counter the suggestion that there could have been cities at e.g. coasts tens of thousands of years ago, but the fact that they seem to be so frail in the beginning points out that it's not also improbable that first "higher civilizations" were indeed the ones we know of.
I’m also not convinced that people would leave a city for a subsistence life in the country en masse. There are several factors working against that like lack of knowledge and skills needed, the good cleared land already being inhabited, and moving too far would put you in a region where you don’t speak the same dialect and would be seen as an interloper by the local people.
Apparently distance wise at least it wasn't very hard to escape from the grasp of earliest cities and the place where you went - a days walk away - likely was not that different - "Assuming draft animals and carts on a flat alluvial plain, the reach of the earliest states for grain requisitions is unlikely to have extended much beyond a radius of roughly forty-eight kilometers"
Of course leaving ones home is probably a burden if you've used to sedentary life.
But there may have been primitive agrarian communities.
The origin of the Jubilee was an occasion when all personal debts were forgiven and people could come out of hiding. These would happen every 10 to 20 years, and were necessary to keep the cities populated enough to function.
Actual currency would not be invented until thousands of years later, so money was all about ledger entries recording assets and debts.
The English Queen's recent Jubilee was weak sauce.
I think even without the younger dryas impact, it's possible that early civilization got a reset at this time. When you factor in that the impact would have caused widespread and sustained crop failure, you could easily imagine early agrarian civilization reverting to nomadic hunter gatherers.That's my hunch, but there's little to no evidence supporting this at present.