We absolutely do not - geneticist who has worked on neurodevelopment projects
We don’t even know why Turner Syndrome - a disorder of X chromosomes - often leads to neurodevelopment delays. We have hypotheses that still aren’t tested, so anyone claiming to know the genetics of neurodevelopment is grifting you.
PRS are useful but not definitive when it comes to phenotype development, as you’ve hinted at, but I take issue with using them for eugenics purposes with the main reason being we do not know the underlying causal mechanism. It is too early to use them with confidence for something like this IMO.
I work with PRS and I am not confident in using them for IVF purposes (that may change when we understand what’s actually going on the proteomics level). I would equate it to something along the line of sports betting with the consequences being eugenics in nature.