I ended up starting at programming.dev because someone on HN mentioned it and it at least seemed to have a focus and also wasn't a ghost town. And that was pretty good but I've also joined beehaw (takes some time) because I like its size and decorum and generically would choose to get on their side of a defederation. And after I'm starting to understand how this whole activity pub and defederation and federation works, I really am optimistic about it.
I think somebody needs to build something that's a crossover between GitHub pages and activitypub that sort of behaves like discus and integrates with Lemmy/kbin/mastodon. So that blog writers can have comments at their own sites again and they can integrate together to grow organically. I haven't quite pieced it all together, but I sort of see that could grow as a replacement for what we lost with Google Reader and the loss of blog commenting communities.