A month ago, after looking for a book, I decided to re-shelve of my physical books in alphabetical order by author. In the process, I removed three boxes of books which are now on a table in the living room. After a couple of friends get a look at them, I will donate the remaining books.
This year I am turning 70, so just as at 65, I am giving away any book I do not think I will re-read or use as a reference in the next decade. The exception is the authors I am or have been obsessed with. If I have a complete collection of their works, I keep them all. Dante Aligheri, Hannah Arendt, Vasily Grossman, Mark Helprin, Kazuo Ishiguro, Bernard-Henri Levy, C.S. Lewis, George Orwell, and Timothy Snyder.
I think I had 800 books a decade ago. I am below 400 now. I have many ebooks, but storage for them is invisible, so no problem with wall space. In five years, maybe I will try something else.