For me for example its “Eat me - a natural and unnatural history of cannibalism” by Bill Schutt. Its an amazing book that covers cannibalism in animals and then the history of it in humans (cultural, survival & medicinal cannibalism).
I got a lot of “oh why would someone read something like that?” And “that not something fun to read about!” From relatives but my friends enjoyed the stuff that I could tell them about cannibalism!
One of my favorite non fiction books is “Man and the Mediterranean Forest” by J.V. Thirgood. The author was a forest scientist for England when it still controlled the Egypt, Arabia, and the Levant. It covers the time from the period where North Africa was described by ancient Greek writers as “a land of perpetual shade” through the destruction of the rain forests of Lebanon in 18th and 19th centuries.
It’s been 20 years since I read it and still angry about it. I got it through my library when it was well out of print and somewhat valuable. I filed to have them move it to closed stacks or rare books, but they ignored me and their only copy disappeared a few years later.