I'm only on the fediverse but I miss algorithms. Recommended accounts (which to be fair exists on a corner of Mastodon), similar accounts to one you just followed, custom home feed, suggested posts, etc. Discoverability sucks on fedi and the lack of interest from devs for some sort of private FOSS implementation is disappointing.
Loops was like let's have a "For You" algo early this year but even that seems to be a dead idea.
What about Google Play Services? A pre-installed Swiss army knife of a system app with proprietary code and apps relying on it as a dependency seems to check the box.