It's at least mostly BS. Researchers have found certain genes which have a weak statistical correlation with high IQ but the mechanism of action is unknown. And it's not an additive thing: the interactions and relationships between individual genes must play some role but that has barely been studied at all. There's no guarantee that an embryo with those genes will grow up to be intelligent, or that they won't have other problems. But there's enough "dumb money" in Silicon Valley to provide a customer base of insecure suckers for these startups.

https://www.wsj.com/us-news/silicon-valley-high-iq-children-...

One of the dark comedies playing out in the world right now is that if random physical features are correlated with IQ testing due to co-heritability, users of IVF selection will be imprinting them on their own kids.