@NEETzsche @lain I don't think it's a mistake but rather the "scrobble" usecase is misuse of them. Say you have a "Video" activity, and you have actions against that activity - "Watch", "Rate" - makes sense that you can send a watch or rate so remote server can adjust rating and viewcount accordingly, the "scrobble" usecase is more of a side-effect - since you know that user sent a "watch" you can show what latest video they've seen, same with rating.

Now you're taking this side-effect and making it a "main purpose" and referencing documents that are not even on the network, say you send a "scrobble", i.e. "Watch" for a youtube video or some brand new video platform that competes with youtube (that is not federated). The side-effect remains (you can show the last watched video in the UI) but main purpose becomes invalid, not only it makes no sense from AP perspective to "Watch" nonexistent entities (think of it as of "Like" for nonexistent post) but it also can be a burden on servers, i.e. if server IS configured to track "Watch"es, it could as well behave like this
>oh i got a "Watch" for a youtube.com/watch?=rickroll
>i'm not aware of that video, let's query youtube.com instance
>oh i got invalid response uwu i guess we'll see next time

So to avoid confusion and spamming, in my opinion this "scrobbling" thing should instead be completely free-form and user-generated and purpose-built around the UI (showing a second line under user's name/handle). We'll have something that isn't referencing anything that's supposed to be on the network (it's an "original" document like ubiquitous "Note") and we are not relying on the side-effect.

Bonus points for being able to re-use existing APIs and adding an option to "post" as a "ongoing activity" from PleromaFE as well as exposing it as an oauth scope, so that i.e. you could authorize Steam/Discord/ListenBrainz/whatever to "post" this presence for you but not have access to regular posting nor anything else. Everything would be better than current esoteric knowledge of "using a script for importing your scrobbles from lastfm automatically"