The way Lemmy works right now is you search a community in your instance for it to then get shown, so you need to first discover that community from elsewhere. With that in mind, what are some growing communities that you discovered that could get some more love?
The short answer is no, you dont.
Think of this like email, you sign up to a mail provider (gmail, yahoo, fastmail, etc) or even if you’re feeling up to it run you own email server with you own domain. You can then use that account to send emails to anyone regardless of which provider they picked and anyone can send you email too.
Lemmy (and ActivityPub, the underlying protocol) works the same. ActivityPub under the hood even uses the same concept of an inbox and outbox. You pick your provider and you can comment, post, etc. to anywhere regardless of which instance the other users or community is on.
If you see a post on another instance (e.g. Beehaw) you can just comment in the webui or app and it’ll just work.
I’m wondering, does ActivityPub have a way to delete content such that the deletion is propagated to other instances?
Yeah it does, when you delete some content it creates a “delete” activity which is sent out to all the servers that content was shared with. Those instances should remove the content on their side too, of course there is no way to ensure the content that has been shared is deleted, but activitypub does have a mechanism to delete content that has been federated.