Going forward, there will be a new Reels feed that includes videos that your friends have liked or commented on, so you can see what your friends have watched and what they like. Your friends will also be able to see the videos that you have liked, which is something to be aware of.
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Instagram used to have a dedicated Activity feed that offered up this information, but it was removed several years ago. It is not yet known if Instagram plans to provide an opt-out for the new feed.
This is a bit terrifying privacy wise. I've heard dubious things back when the activity feed was a thing about how it was used. This feels like a recipe for outing people in personal ways they didn't expect, especially after they probably got used to Instagram likes not being exactly anonymous but close enough as they didn't get disclosed to other people.
Long story short Activity Pub only pulls the content it needs from remote servers when it needs it and can choose how to handle media (serve the original or cache and proxy). It already is similar-ish to a CDN.
AT-Proto is super complex, but my understanding is that a new server (app in AT-Proto parlance) needs to copy everything beforehand from all others, and needs to constantly replicate everything, wether it will be served or not, making the data transfers intractably massive.