I have someone who claimed our local mask mandate stopped exponential growth, since I pointed out there's no statistical correlation with thr mask mandate. He said it prevented exponential growth.

I highly doubt that. Contagions like this arent exponential, since there's always barriers to infection. On top of that, most of our population is already immune at this point. We're at the tail end of this wave, no matter whether you wear a mask or not. There aren't enough people remaining to keep the high numbers of infections up.