TheZ posted this with their books, and I thought I'd have a look to see what mine would be.
My 100 least popular books read according to GR
There are a lot of non-fiction (some very niche, unlikely to find readers unless they're really into the topic, or if the author is their grandfather - book 1, lol), a lot of books read for reading challenges, and a lot of Dave Duncan, who should be much more popular, IMO.