I don't think many people are aware of the purported causal relationship between fertility rates and infant mortality. I wasn't for a long time. I've read different studies where the author/s conclude it's true and other studies where they say this public health tenent is less set in stone. Because there are conflicting views, I don't 100% subscribe to it. There is however evidence that Bill Gates and WHO have been involved over the years in producing questionable vaccines, some of which have resulted in decreased fertility or sterilization.

https://fcpp.org/2020/07/19/gates-who-and-abortion-vaccines/

https://www.scirp.org/journal/paperinformation.aspx?paperid=81838