in 2018, Facebook told Vox that it doesn’t use private messages for ad targeting. But a few months later, The New York Times, citing “hundreds of pages of Facebook documents,” reported that Facebook “gave Netflix and Spotify the ability to read Facebook users’ private messages.”
Surprising? No. Appalling? Yes.
If you want private messaging - use Signal.
If you use any kind of messaging on commercial platforms, expect immediate loss of privacy. They call them “direct” messages for a reason.