Ask HN: What communities are there for discussing good books?

For fiction books (and some nonfiction) there is good "rotten tomato for books" https://bookmarks.reviews/

there is not a lot of discussions there, but maybe it satisfies your need.

I wish there was something like this for business books

On reddit there are a couple of great subreddits where people discuss and present excellent books

https://www.reddit.com/r/books/?st=JRYREWUL&sh=3e5709bc

I'd definitely recommend checking out Goodreads. There's a lot of great niche groups, as well as following other people with similar interests you can discuss books with them in your feed.