I think that hypothesis needs to be challenged or at least framed differently, since there aren't that many examples of civilizations that "reverted" to nomadis

I think that hypothesis needs to be challenged or at least framed differently, since there aren't that many examples of civilizations that "reverted" to nomadism from an agrarian society (it would probably be more accurate that climate change/human activity dampened agricultural output enough that nomadic peoples became more prevalent as the population of agrarian peoples collapsed/migrated elsewhere), at least outside larger contexts like the Bronze Age Collapse where there was a centuries long period of population decline in a large geographic area. And in more recent centuries, "collapse" is almost always synonymous with political turmoil/change while the peoples remain in place. I think that's important too, because we're not seeing so much of a "collapse" of our global civilization, but migrations of peoples across it, and a rise in political turmoil as a second order effect.