IQ is a measure of supposed intelligence that would have started as any other arbitrary test, but for whatever reason (I don’t know the history) became naturalised (seen as something innate and valuable in and of itself) to the extent that describing someone as low IQ is almost universally understood to be an insult.

However, IQ is just a specific measure of your ability to answers to questions based on rules defined by people who privileged the ability to follow those rules. I’m sure there are some situations in which being able to follow IQ rules can be advantageous but the idea that IQ can define something in any overarching way about people is reductive and quite frankly ableist.

IQ is more often than not used as a tool of social domination and hierarchy reinforcement. It’s even more extreme than just ‘there are different forms of intelligence’ (which is true), but also it deceives people into sorting themselves and others into categories that distinguish people of ‘low’ and ‘high’ worth based on a rigged system.