This depends on the subject of the book, but there are enough books written pre-1970 (or some other year one is comfortable with, before the era of “book spinners”, AI etc) to last multiple lifetimes. I used to spend hours and hours in bookstores, but so many books these days (AI or otherwise) don’t seem that interesting. Many, many books could just be 3 page articles, but stretched to 150 page books.
So yeah, simply filtering by year published could be a start
Buying a book scanner and frequenting used book stores seems like a past time to start that'll pay off in the long term.
I enjoy old fiction enough that sites like gutenberg.org has that covered and I barely bother with trying to find anything new that I want to read, and that began long pre-ai-slop so no real change for me.
For non-fiction it is a bit trickier. I buy DRM-free from some niche publishers, but I have no idea which ones can be trusted to not begin to mix in AI slop in their books.