This for me is one of the last great unsolved problems on the internet. I've yet to find a book recommendation site/algorithm/social thing/whatever that actually works well enough for me to trust it and invest my time in logging my own reads to improve the results etc.

I've had far more success personally in growing my reading list with books I ended up loving by following a few people on Instagram who share their reading groups choices. Similarly, anytime anyone whom I vaguely trust recommends me a book I just order it immediately on Amazon and add to the input pile.

It's vitally important for me to keep the next read pipeline well stocked - I get through a lot of books, and if I run out for whatever reason it can take me weeks to get the habit going again.

Virtually every other form of media, I can find a recommendation system that works well enough, even if it's not perfect. Books have always been an outlier for me personally.