IQ does show differences between the races. However, this isn't evidence that white supremacy is correct. It's evidence that IQ testing measures culture when it's supposed to be measuring biology.
Race is constructed. Genetic, evolutionary, anthropological, and archeological evidence all point to shared ancestry and kinship. All the people's of the world aren't separated by near enough distance or time to explain a significant biological difference. And that's ignoring the wide interbreeding that was always a thing. Remember Rome was cosmopolitan empire. Many of those Roman soldiers who marched down the first paved roads of London were swinging black cocks.
So what can we make of a so called "objective" measure of a "biologically determined" trait that hews to culture above biology? This isn't just a bias that needs to be tweaked, the whole concept of biologically determined intelligence is a reification fallacy and IQ as an instrument is hopelessly broken and should be abandoned.