The Flynn Effect (IQ is rising ca. 3pts/decade) encompasses at least the silent generation, so if we accept the proposition that generations before that probably did not have a higher IQ - because there was less intense education and less knowledge available and needed for normal functioning in society - then (at least in developed countries - in less developed countries which haven't plateaued yet the Flynn Effect seems to be still in effect) the generation with the highest IQ were the millenials.

The numbers are not 100%, because these things develop slowly, and there seems to be divergence between Internally and Externally Scaffolded Tasks (externally are those where you get all needed information and have to come to a conclusion, things like series of symbols or numbers; internally are the tasks where you need to generate the relationship yourself, drawing on language, memory, and abstract reasoning, e.g. "In what way are Justice and Fairness alike").

In developed countries, with internally scaffolded tasks the growth has been continuing (although a bit slower), but with their external counterparts there is a significant decline to be seen since the turn of the century.

This was deposited in front of the US Senate. The blog entry of the responsible researcher is available here: https://thedigitaldelusion.substack.com/p/i-told-the-senate-gen-z-is-less-cognately