Mice models for Alzheimer's research may not be as valid as thought though. I recommend reading this open-access book chapter on the topic: https://brill.com/view/book/edcoll/9789004391192/BP000025.xml

Have you considered asking for this thesis advice the Effective Thesis? They probably can connect you w/ someone w/ a background in this area.

[Below are my (totally optional) thoughts on this (and I'm only a software engineer working in a genomic research institute w/ no formal biomed background):]
I would think that (ethically approved) studies on humans are more useful in general, as they translate better to other humans. Also, the more we try to reduce and substitute non-human animal experimentations w/ alternatives, the more there is incentive to develop these alternatives. I must admit though that I'm "biased", as I consider non-human animal suffering no less urgent than equivalent suffering of humans, other things being equal.

(No biomed background, just an avid reader of science news) Maybe you already ruled this out based on your specifics, but could lab-grown mini-organs be a suitable third option for your experimental ideas? That in-between choice might offer an end-run around both the mouse-to-human translation problem and the overhead and slowness of experimenting with human subjects within the time frame of a Master’s. Caveats: your estimate of the moral status of mini-brains, the smaller existing knowledge base of how to care for them and interpret results, and possibly cost. I don’t know if there are existing mini-organ models for Alzheimer’s as there are mouse models, sorry.