The "reverse Flynn effect" is something that's been observed in a small number of Western countries that do IQ tests as part of their military conscription.

But for example, in Denmark, when plotting measured IQ against first name, we observe that there is cultural effect, that would explain that the "reverse Flynn effect" is simply an averaging down, caused by the import of migrants from lower IQ regions. The "reverse Flynn effect" is not observed in Singapore, for example, which has maintained consistent high IQ over many years.

https://emilkirkegaard.dk/en/2019/06/article-out-first-names...

You didn’t ask me, but (aside from the effects of tech and social media) my #1 hypothesis is the rise in single parenthood. Parenting is so hard that I doubt pretty much everyone’s ability to do it well on their own.

Nope. For all I know it’s due to the sins of the people. The reckoning of heaven.