I heard about The Mushroom at the End of the World from this Sophie from Mars video called "The World Is Not Ending", which talks quite a bit about mushrooms, and doomerism, and quotes frequently from this book.

I don't read a lot of non-fiction, but this book quite deliberately and explicitly structures itself in a rambling manner, interspersing history and anecdotes, with tangents galore. Rather than some formal thesis and organized argument, this book paints a series of encounters with matsutake mushrooms in varying contexts and perspectives, with a thematic framing.

If I had to sum it up, the book posits that progress (and even hope) are part of capitalism and its need to scale and organize and alienate; if we are to thrive in the decline of capitalism, then we need different tools that often fall in its margins: noticing, unpredictable encounters, new relationships, and more mutualism.

I also enjoyed this review which gets at all of this much better than I can.