Hey, I am currently trying to understand a bit better what the Activity Pub allows and what it doesn’t as I am preparing a presentation on that topic.
On Lemmy I can join other servers without having to recreate an account. Does that also work for across Activity Pub supporting software? Could I join a PeerTube page and then post there? Could I upload videos? Could I join Mastodon or Pixelfed and post images?
With lemmy account you can only join “groups”, so other Lemmy communities, or equivalent piefed or nodebb.
With a Mastodon account you can also join groups (Lemmy etc), but you can also follow single accounts from any mastodon, pixelfed, peertube etc instance.
Why then having a Lemmy account? The interface, how you see the posts, depends on the software. Lemmy is reddit-like, mastodon is twitter-like etc
If you want to upload your video to a peertube instance, then you need an account on that instance
Also, mbin allows you to follow individual users as well as groups.