The issue is basically with the word itself. "Race" as it is used in policy discussions is almost purely a political construct, that tends towards being self-defined.

An actual biological race is something we can find, but you can't use it for political policy because there's nothing about a biological race that gives a deterministic outcome to behavior.

This is because all behaviors are both partly genetic, partly environmental, and even environment can effect genetics. As you've pointed out, you can't get higher IQ with malnutrition.

The effect of Leftism on IQ has been identified, but is even more quietly buried than a link between race and IQ. This is because Leftism leads to starvation, violence, low-trust, poor education, so on and so forth. If you take a population of people and expose them to Leftism for a generation or three, the statistics are grim.

A good example of this is the 1 SD IQ difference between East Germans and West Germans after the Berlin Wall fell. To be clear, these are effectively the same people by any biological means, but Leftist policies are so poisonous that they damaged everyone to a severe degree. Consider that the lockdowns, which only went on for a year or so, caused IQs among American children to drop by 20%