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.
Look for YouTube commentaries and blog posts. There aren’t as many blogs in general as there used to be but there were loads that focused on lesser known books, translated books, etc, and some will still be around. There might not be lots of comments, but the blog post itself will be fairly comprehensive.