Terry Pratchett's novels may have pointed to his dementia 10y before diagnosis (opens in new tab)

No need for someone to be an author:

> People generate vast amounts of written material through emails, reports, messages and online communication. With appropriate safeguards for privacy and consent, subtle changes in writing style could one day help flag early cognitive decline long before daily functioning is affected.

At work:

   From:  HR-AI Termination Services
   Subject:  Please return all Corporate property immediately

At home, you are suddenly deluged by ads for anti-amyloid drugs.

(Yes, in a kinder and gentler world, things would be handled rather differently):

I remember reading 'Raising Steam' with more and more alarm and dispair. I loved all the other books, and there was something so obviously going wrong mentally in this book. Dementia sucks.

Strangely, 'The shepherds crown' was much less impacted, even if wikipedia places it a bit later in the timeline.

> With appropriate safeguards for privacy and consent

Oh, boy. That's too enormous of an unsolved problem to just handwave away like that.