If it’s not a famous book, you may find some Goodreads reviews and if you’re lucky a Reddit post or two, but not vasts amount of online discussion like you’ll find about any passingly good series or movie.
And if you love a movie or a tv show, it is much easier to convince people in real life to also watch it, since it’s way less time consuming and not everyone even reads books, but most people watch movies.
I just think that this really sucks about reading books.
Most recently it’s just my favorite guilty pleasure book series, the Empress of Rome series, lol. I’m not gonna recommend it to people here on Reddit necessarily cause it includes a lot of things that Redditors wouldn’t like (Idk if that’s different on this sub). But I have this all the time when I finish a book.