and it's usually found to have a nonnegligible, positive correlation with IQ
It's interesting you mention that because despite Rudyard claiming to have such high trait openness which would imply that he's incredibly intelligent, he's objectively not intelligent.
Rudyard claimed starting around November/December of 2023 and onwards that he has an IQ of 110. Furthermore, he adds that he's not sure if it's correct because it was a 'really bad period of [his] life'. The obvious implication is that he thinks it's higher because in no way would a negative environment increase IQ. On top of that, it's highly unlikely his IQ would be diminished significantly by a bad period of his life unless he had severe malnutrition, highly significant lead/chemical exposure, zero education, or was subject to extreme emotional abuse as a child, as those are the environmental factors that would significantly decrease IQ more than a couple points.
The problem with this 110 IQ claim he makes is that this isn't the first time he mentioned his intelligence (or factors associated with it). In June of 2022, over a year before making the first 110 IQ claim, he says that he has a 'lower than average' IQ in his video titled, "10 Taboo Questions About History and Society". Besides that, in a tweet from 2020 he says he has 'average IQ'.
I'm far more inclined to believe this over his tweets not only because he released this much earlier than them, but also because other evidence points to his lack of intelligence as well. In the video, he claims he scored poorly on his SAT and his school grades, which while not as strong a correlate to intelligence as IQ is, still points generally to a lack of intelligence. In the video as well, his only evidence that he is intelligent is that he has a 'photographic memory' (I'll get into that soon), that he can write video scripts off the top of his head (???), that he reads a lot of books, and that he dropped out of college because he had a successful youtube channel, all of which are poor evidence.
In this next video "Why did the School System Fail?" he claims he did poorly on the subtests relating to mathematics, spatial ability, and shape-moving, which were what most of the IQ test was, rather than what he claims to be good at like 'empathy'. The problem he has is that he gave the exact evidence as to why he's unintelligent in trying to prove he's not. By mentioning that he did poorly on those specific subtests, which he himself says disproportionately determine the result on the test, he objectively describes why he's unintelligent: he is bad at the tests most correlated to actual intelligence. His primary strategy to cover up his lack of intelligence is to obfuscate about the entire concept of IQ by claiming it can never be measured.
On a side note, relating to his 'photographic memory', it can be seen from the video above that he restricts the claim down to a photographic memory for 'sounds and maps', which raises doubts about the validity of such a claim. Given that he described his 'photographic memory' as being able to draw maps from any year in history, it is much more likely that he doesn't have an extraordinary memory but just that he thinks the very act of remembering something in detail is a photographic memory.