Last.fm scrobbling
The official Spotify clients and spotifyd will scrobble currently playing tracks appropriately using the official last.fm / Spotify service. Possibly, implementing the "Connect" feature tracked in https://github.com/jpochyla/psst/issues/33 will automatically implement this feature as a side-effect, as this suggests:
...Spotify changed the way their Last.fm integration works. Scrobbling now happens on Spotify's servers, rather than the client, so all Connect devices can now scrobble.
Workarounds: using a local MPRIS based scrobbler, such as scrobblez. EDIT: blocked by https://github.com/jpochyla/psst/issues/368
I don't believe you get any scrobbling by implementing Spotify Connect. ~I don't think you get it by implementing the reporting/event-service stuff either (see https://github.com/librespot-org/librespot/issues/913, https://github.com/librespot-org/librespot/discussions/626), I thought each client-side scrobbled directly, but I might be wrong about that.~
Edit: Scrap that, I just saw your link, it must be server-side... So maybe it is the reporting/event stuff. I don't think it's part of Connect because librespot provides Connect and nothing gets scrobbled when using that.
Workarounds: using a local MPRIS based scrobbler, such as scrobblez.
Such scrobblers do not work on MacOS. So implementing one to psst would be a good idea.