I’m kinda new to this - so what you’re saying is the mouse model induces beta-amyliods directly, rather than finding ways to give mice Alzheimer’s, whereas the human tests are for humans that have Alzheimer’s? Meaning we aren’t doing any tests of simply stimulating BA growth in humans?

Which is not the point of the research paper: the point of it is they've targeted a novel mechanism (waste clearing) and observed two effects impacting markers for Alzheimer's.

Amyloid beta might not be causative, but if you hit a mechanism then it stands to reason it might be indicative - in this case if Alzheimer's is partly or fully caused by a waste removal problem in the brain.