While I agree with some of the things said, the last sentence where you started to imply that neurodivergence can be caused by external factors is completely false. These are physical differences in brain's wiring.
Not sure about autism, but ADHD is one of the most studied disorders and you can pick it up with a brain scan, like MRI and other methods (currently imaging methods aren't typically used for diagnosis but it's plausible that some day it will be)
Physical differences that no test can detect?