One of the more comprehensive treatments of the Depopulation problem Elon Musk is so panicked about and seeking to solve himself by impregnating as many A-list Vaginas augmented with fertility drugs as he can, but still IMHO under-estimating how rapidly the population will drop once the energy to produce FF based fertilizers becomes in short supply, unavailable or too costly to produce food for billins of "Useless Eaters".  At some point in the next 20-30 years if not sooner, between climate change, depleted topsoil and subterrainean aquifers, and/or monoculture crop failures due to blight, along with the lack of fertilizer we will run into a global famine that will wipe out 1/2 the global population of Homo Saps in a single growing season.  The resulting anarchy and failure of transportation systems and energy production and delivery systems will wipe out 1/2 again the following year, and this rapid exponential collapse will look like the collapse of the deer population on St. Matthews Island.  By the time this cascade stops in 5-10 years, the remaining population across the globe will likely be perhaps .01% of the peak population when it begins, say 1 in ten thousand will make it through the population bottleneck.  So if we start at 8B, we end this at 800,000 human souls still walking the earth before we might begin to stabilize and rebound.  Or we might just keep on going until the last surviving Breeding Pair of homo saps dies 10-20 years later and we go the way of the dinosaur and dodo bird.  If I do last until this cascade begins, I'm sure to go in the first few weeks when the food runs out and the CNAs carve me up for dinner, at my request.  All I ask is that they make it quick and as painless as possible.

The falling birthrate math is just a mind of pacifying propaganda to let people believe that we'l disappear peacefully and quietly, slowly drifting off into the sunset because we don't breed enough replacements, not because we'll start dying by the truckload, and they will be one of the people scrounging for food or eating their parents or kids at the end.  The likelihood that we go slowly into this good night is very small.

A little hopium though keeps the people from panicking and the Children of Men scenario from starting too soon.

https://www.bloomberg.com/opinion/articles/2024-03-10/global-population-collapse-isn-t-sci-fi-anymore-niall-ferguson

Global Population Crash Isn't Sci-Fi Anymore

RE