There’s a reason why apps like Signal exist. It’s open source and you know what’s in the code.

Meta/Google etc all have its revenues directly linked to data they can gather from you. I don’t have much faith that things closed source that they wrote are completely hands off at that data right in front them.

Certain things are believable like them not sending all your messages back directly. Impossible to hide that from the sheer volume of data that would have to be sent through the control channels. But it doesn’t mean that local data stored in the app isn’t analysed in some way.

Meta controls the actual app and any updates to it. There's no telling if there's code that searches your message history for specific words and sends info back to Meta through control channels about your interests. Eg you chat with a friend about IKEA and potentially Meta knows that you're interested about furniture without any of your messages being read at Meta central.