The FDA scientific advisory committee
rejected Biogen's claims in a unanimous vote. (Note that Biogen actually claimed in its application that aduhelm ameliorates Alzheimer's). The history of the aduhelm approval process just has a stench about it; you can see earlier posts by this author on the topic (linked to in the original article) to see some of that come out.
> Have there been any studies that show that plaque-reducing drugs don't ameliorate Alzheimer's?
There are, I believe, about a dozen drugs that tried to reduce plaques that have all failed to ameliorate Alzheimer's. And several of them despite actually demonstrating reduction of plaques.