The amyloid hypothesis is still the top candidate for at least a form of Alzheimer's. But yes, the issues with one of the early studies has caused significant issues.

I say "a form of Alzheimer's" because it is likely we are labelling a few different diseases as Alzheimer's.

I went searching for more info on this and found https://www.science.org/content/blog-post/faked-beta-amyloid... which was an interesting read.