The world's population should be at most 50 million.

[Hammok Man]

I do not think there is going to be an upper limit on human population period. Growth and expansion is part of human nature. The low birth rates in developed 1st world nations is a function of supply and demand. It cost more today to raise children than in the 1960’s.
https://247wallst.com/investing/2011/06/...e-a-child/
I am of the opinion that most families will have as many children as they have reasources to support.

Also, women are more inclined to enter the work force in professional careers, there is a trade off to this when it comes to having children.

Lower socioeconomic populations are having more children in the developed world, I think this is mainly due to government social programs. Once again the number of children is equal to reasources available.

People have been saying for a very long time that population pressures are going to lead to world wide shortages of commodities. I am unaware of any trends that indicate this. world population has almost doubled from 1960 (approx) rather than rationing and shortages commodities are less expensive and more plentiful.

https://www.caymanfinancialreview.com/20...ty-prices/

Also fifty million people is not a lot, I think you need to go back to the pre Roman era to find that sort of low population density.