Thank you that is useful to have that explanation here. I had no idea it works like that!

I’ve not seen this type of logging in issue within the Mastodon ‘world’ because no one’s ever ‘sent me a link from another instance and then I tried to log on from that link’ 😂. I just tried it on an inprivate browser window and of course it’s the same as what I found here with Lemmy - as you described. With Mastodon I’m on the .social instance and I can see and interact with posts from any other instance - but after your explanation I realise that’s because the content was alwasy served up from within the instance.

[I agree that with ActivityPub we certainly cannot expect to log in with the same handle *between *services (i.e. use your Mastodon handle to log in to Lemmy). Although that would be cool. Persistent IDs across the fediverse would be the dream imho (like Nostr does it).]