IQ and other psychometric assessments are not actually backed by hard science but vibes

so when someone brags about having a "genius level IQ", just write them off as a narcissist

sincerely, your local psychologist turned software engineer

humans and other animals are complex systems, while there are diagnostic tests which measure a degree of performance in specific skill areas, you can't really boil someone's intelligence down to a single number: the person who sucks at math might be a great strategist, for example
@ariadne There's One Number mainly because racists insisted on there being One Number. Early on, there were multiple different theories of measuring intelligence (and later 'giftedness studies', once again, broke the One Number apart), but Spearman's "g factor" became the dominant one because it appealed to the "Race Scientists" of the early 20th century.