A study in Canada was published in 2019 looking at the differences between 2 neighboring cities where on stopped fluoridating water in 2011. They saw that saw a significant increase in cavities in children in the city that stopped fluoridating vs the other. This is despite the fact the the city without fluoridation actually has somewhat higher adherence to brushing, flossing, and going to the dentist. No difference was seen yet in permanent teeth, but that's because the study would need more time to see effects there.

https://onlinelibrary.wiley.com/doi/full/10.1111/cdoe.12685

Of course, we still should do more studies on fluoride neurotoxicity. Most studies look at levels of fluoride at 1.5mg/L or higher, which is more than double the recommended level by the US (0.7 mg/L). There is a hard limit in the US of 4mg/L, but the EPA strongly recommends a limit of 2mg/L. This only really matters for locations with very high levels of fluoride in the groundwater, and is thus quite rare. The EU's limit is 1.5mg/L.