These days I use
https://kulli.sh as a meta comment aggregator on interesting links that I find on HN and a few other places[1], and this helps me find other like-minded communities that are sharing and commenting on similar content. I posted an article about how this works in practice for me last year[2], and I'm still pretty happy with this workflow both for content and community discovery.
[1]: Mostly niche subreddits, Lobsters, Tildes, a few Discord servers and forums
[2]: https://lgug2z.com/articles/finding-interesting-comments-dis...