@TheRedSpade@Teknevra If I understand it correctly, a Fediverse account (e.g. Mastodon) can be used to create reviews (about films, music etc. from the database). And these reviews can then also be shared and commented on in the Fediverse.
It isn't federated but I use Trakt to manage watch lists and scrobble my viewing history from Plex. There are some discovery features and a minor social aspect.
They have an API available so I could siphon off my data if I wanted to but then I would need to build something like it to use said data in. I'm good.
This isn't really what you're looking for, but libremd is an Invidious-style front end for the IMDb. It manages to scrape quite a bit from them, though not everything.