IQ tests as part of the hiring process aren't illegal in the US, but they aren't used because it puts the company at risk of discrimination lawsuits.

The validity of IQ tests is debated and their history is checkered: they've been used by eugenicists and racists to support their views and statistically minorities under perform on them.

It's not hard to imagine someone purposefully writing an "IQ test" that's racially biased by focusing on things that wealthy white men know. An infamous example from the SAT in the 70's (and allegedly used later as well) that favors those familiar with rowing (aka: "crew"), a largely Ivy League sport:

RUNNER: MARATHON A) envoy: embassy B) martyr: massacre C) oarsman: regatta D) horse: stable

So it's fine if hard tech interviews are actually trying to assess your IQ, but if they're racially biased it's a problem.