Welp, if you’re not interested in doing a read for read with other writers, the best place might be to simply post it on Wattpad or a similar site and let ordinary readers tell you what they think of it. You could put a note in the book description that you’re looking for honest critique, or put that at the bottom of each chapter or something.
If you are interested in read for reads, there’s a thread here for that, and possibly other threads where they do that too. ¯\_(ﭢ)_/¯