IQ levels are same as before, it's just easier to spot differences.
Much as with some other widespread phenomena that come to mind, it's an observed trend the reverse of what might otherwise be expected.
Theoretically this effect would wear off with the next generation, unless there was durable damage to genetics that gets passed on. A cursory search suggests this may be possible, but I’m not a biologist or geneticist.
Those might be behavioural, cultural, environmental substances, information/media stressors, or others. More research is needed....
As I click another AI generated ad to tell which company could possibly have so little integrity…