I thought the understanding for base rates of autism was that people are living longer and starting their lives later. Becoming financially stable later, having children later. Having children later rather than earlier significantly increased the risk of autism.
After that then the question becomes about intensity of autistic symptoms, where the base rate of autistic children makes sense given the data, but the intensity and thus increased likelihood of seeking diagnosis may be increasing as a second factor which sits on top of expanded diagnosis standards.
For intensity, there are suggestions that maybe obesity, plastics/chemicals could be contributing, but it sounded like there wasn't enough data on it.
I'm not sure what other answer they found. RFK has said he doesn't think people should follow his personal health advice. He knows he's neither a scientist or a doctor and supposedly there was some team of scientists working on it. I'm not prejudging that they can't have arrived at some useful result, but it's obviously very politicized.