"Alzheimer’s is driven by the buildup of toxic proteins called amyloid-beta."

That's the predominant theory, but nothing affecting them has yet proven to be efficacious so far (AFAIK).

Likewise, at one time everyone "knew" aluminum was a culprit, because it showed up in autopsy analyses of affected people. However, it turned out that correlation wasn't from aluminum causing it, so avoiding aluminum didn't affect the disease.