I had seen that one..it is curious and led me to speculate vaccine uptake vs IQ might be an arc.

That said, at least according to this paper, the correlation is monotonic, see figure 2.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8133799/

If we take it as a given that vaccine hesitancy was the "right" answer it suggests a strong confounding factor (brainwashing or herd following being correlated with IQ?) and/or the paper is simply bunk and reflects the author's biases.

P.S. - albeit IQ and educational attainment are not synonymous but at least up through IQ +3 std devs I'd guess they are highly correlated.