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.
This is part of what got me into fantasy books. I never cared for them tbh but a friend recommended the first mistborn book and on my old account I posted updates on the Brandon Sanderson subreddit and they were so welcoming and encouraging. Got me to read a lot of the rest of his stuff and now I’m into fantasy as a genre