[0] https://en.wikipedia.org/wiki/Flynn_effect#Possible_end_of_p...

https://www.nbcnews.com/think/opinion/iq-rates-are-dropping-...

This is fairly well documented. Average IQ scores in France have been declining a couple of points per decade if I recall correctly...

I believe mass immigration from low IQ countries and dysgenics are often sourced as two of the potential reasons. But I have no idea how true that is.