> Giving an IQ test for a job is illegal.

No, it's not. Using any criteria that creates substantial disadvantage to a protected class is illegal if you can't show a sufficiently close nexus to bona fide job requirements/performance, which happened to be found to be the case with the IQ test that was adopted as a direct replacement for overt racial discrimination in the Duke Energy case. But the legal rule that comes from that case is not “IQ tests are illegal”, and in fact IQ tests are used in a number of places in hiring (including, as became notorious in another case where the practice was upheld, being used where a score above a threshold was disqualifying in a particular police department.)

The algorithmic questions used in software engineering interviews are just glorified IQ tests imo.