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.
You might think about starting a reading club where you meet periodically and people discuss what each of them has been reading. With a book club, everyone reads the same thing but what I’m suggesting is you could get together and each person gets to talk about a book and how they related to it. Just a quick summary of the book because each person has to be willing to listen to the others, but then you can talk about why you felt connected to it, or what it evoked in you.