Dawkins hasn't been relevant in the field of evolutionary biology for 15+ years and I don't know why people pay attention to whatever he says just because he built a brand about being an an edgy atheist.

There are literally dozens of arguments as to why 'eugenics' (beyond very basic hanging fruit like eliminating monogenic diseases etc.) wouldn't work and doesn't make sense to begin with and many of them have been spelled out in the tweet's replies and blog posts, I'll let you do your homework.