Activated charcoal is a supplement. It’s been used for centuries to relieve poisoning symptoms, to absorb anything and everything that may be causing stomach upset.
Whether you have neurotoxicity, fluorosis (teeth stains from excessive fluoride), or you want to avoid these things, you can eliminate fluoride from your life (with difficulty). In case you do not have the means to rid your world of fluoride, unfortunately you cannot filter it out of your water.
According to ThoughtCo, you can use reverse osmosis, activated alumina, and distillation to filter your water of fluoride. In that case, it may be easier to purchase bottled water (I know it’s bad for the environment), move, or detox. Here’s how to do the last thing.