Their mobile app most likely records everything being said and transmits it encrypted to their servers, so that they can improve ad targeting.
“Ah, but there’s an undetectable binary blob that gets linked in and called without being detected by anyone working on the code,” you say. In that case consider the battery life impact. The power consumption of the Facebook app compares favorably to its social media peers. Is everybody else also recording, encoding and encrypting all the time?
Such as?
Facebook has explicitly denied spying on people's conversations. I can't think of any situations where they have flat out lied about something like that, so I'm curious to hear what conspiracy theories they have proven true.
It’s a complete mischaracterisation that Facebook shared private messages with Spotify. By the same logic, you could say Google is sharing your emails with Apple when you access Gmail using the iOS Mail client.
Spotify was offering an integrated client to FB’s chat service. This UI integration was a market failure and was discontinued years ago. Of all the things wrong with Facebook, this wasn’t worth the noise.
Shadow profiles for example.
Scrolling through a social media feed is a heavy activity on a phone (which may be surprising because it seems passive). Constantly fetching more data from servers, decoding incoming images and videos in background threads, shuffling data to GPU-accessible buffers for fast scrolling, etc. — There’s a lot going on all the time when you’re scrolling mindlessly.
So what? Thousands of the same people have access to the full source code of everything underhanded Facebook do and it hasn’t stopped anything.