The meta analysis you linked ( https://jamanetwork.com/journals/jamapediatrics/fullarticle/... ) specifically denies any noticable associations with fluoride at the levels recommended in countries that add fluoride to water.

  For fluoride measured in water, associations remained inverse when exposed groups were restricted to less than 4 mg/L or less than 2 mg/L but not when restricted to less than 1.5 mg/L

  There were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L.

The meta analysis you linked gets the strongest results in areas of the world with outstandingly high levels of fluoride and other elements in the ground water .. water with so many additives it rings like a bell when tapped with a hammer (okay, that's an embellishment).