Interesting to hear someone articulate this dynamic. I do not believe my father has dementia but there are similarities in regards to “repeat of the same conversations”.
You might want to read Drop Acid by Perlmutter, stuff about sugar by Robert Lustig and maybe Fiber Fueled by Bulsiewicz. They give pointers to why Alzheimer might happen in the first place and how to avoid it. Those are life-long advices.
There are no cures; but there are treatments that can delay onset, slow progression, and improve quality of life to varying extents depending on which disease.