It seems especially bad for the racial realist hypothesis that people who, for example, identify as "black" in America have the the same IQ disadvantage compared to whites whether their ancestory is 4% European or 40% European

I've seen mixed reports on this. Human Varieties, for example, has a series of posts on colorism which finds a relationship between skin color and intelligence in the population of African Americans, as predicted by both the hereditarian and "colorist" (i.e. discrimination) theories, but does not find a relationship between skin color and intelligence within families (as predicted by the hereditarian but not the colorist theory), and I know there were studies using blood type which didn't support the hereditarian theory but appear to have been too weakly designed to do that even if hereditarianism were true. Are you aware of any studies that actually look at genetic ancestry and compare it to IQ? (Self-reported ancestry would still be informative, but not as accurate.)