Book recommendations are good. I really liked the SuggestMeABook subreddit. It'd be nice to have that here.
I think what those other places are missing are some kind of book club. If there's enough critical mass here, it'd be interesting if there could be small groups read a book together and discuss here.
Tbh I don't know that much about other communities, but I would like to have sth. like a "Let's read together", in order to broaden my reading experience ( mainly reading Hard SF, High Fantasy, and NF).
I don't know how it would have differed from Reddit in this regard, but it would be quite suitable for a forum website to give thorough reviews of books. Some people give reviews of books on Tiktok where they just say the main topic of the book and that it's 'good'... good in what way? And like what other commenters have mentioned, some love too for nonfiction. Maybe we could even have discussions for fanfiction?
I did create c/nonfiction but it's not got a lot going on at the moment. I agree about reviews, for me I post on my own blog and then link it in my Goodreads/Storygraph/Bookwyrm.
I'd love it if we started a small little book club. I actually like reading books and talking to other people about them a lot. And I just think that would be super fun. All the ones that were on Reddit were just so many people talking that I just felt too anxious to even post.
I'd like to see it grow exponentially. i left reddit almost a month ago now and am missing r/suggestmeabook and others. I really enjoy reading many different posts about what people are reading so that I can pick my next book.