Does anybody here can #help me to solve a doubt on #Mastodon and #ActivityPub portability?

Context; I am writing a post about Mastodon and Bluesky and wouldn’t like to be imprecise.

I read in a blog that ActivityPub actually allows moving data of users and content from one server to another and that it is the Mastodon development of ActivityPub which puts the problem of portability.

On the other hand, I found this link where they seem to say that ActivityPub already allows portability but its implementation as W3C standard is still in a draft status. https://swicg.github.io/activitypub-data-portability/

I do really appreciate if someone can tell me if I am reading the issue correctly. I am not a software developer, so I am afraid that I have missed some important concept or info.

Thanks in advance for any help

*edited to add the link (forgotten in the first version)