There is clearly a lack of boards/forums/websites dedicated to product managers. But what I miss the more is a website, when we can get valuable insights about best practices. On HN you can get super useful information about any stack/language/framework by reading the comments, but when you are a PM you have nowhere to get that kind of information
A lot of discussions are unstructured or hard to keep track of. I mean, it's slack, not a forum.
What I'm helping create with the wonderful team at JAM London is a curated collection of 'Hot Tips' with short practical and no-nonsense answers form PMs for PMs. It's picking up interest, looks like your question hit the nail on the head! :D https://www.jamlondon.io/tips/