If 2 is true, then it is not end-to-end encrypted, and I don't think that WhatsApp is lying. They have ways of doing their things without lying, so I don't expe

If 2 is true, then it is not end-to-end encrypted, and I don't think that WhatsApp is lying. They have ways of doing their things without lying, so I don't expect 2 to be true. I think that 1 is the most plausible, however the original post is about "topics they never talk about", so assuming that WhatsApp is the only channel and they don't leak data in other ways (and there are many other ways to leak data), then 1 becomes unlikely. 3 is the most compatible. All the targeting can be done locally, so no end-to-end unencrypted message leaves the app. The app then sends your topics of interests to Meta. 4 again assuming WhatsApp is the only channel, then there is probably some malware somewhere, and it is unlikely that Meta accepts illegally collected data (they can do it legally, better, and with less potential trouble). There are however a few legitimate apps that can do the above. I am thinking about things like predictive keyboards, accessibility apps (screen readers, ...), backup apps (end-to-end encryption is about transmission, not storage), and the OS itself. I don't think Meta controls any of these, and I don't think they would buy data from them (Google and Apple are competitors after all). So I would go for an accidental leak (case 1). For example, for the experiment to be meaningful, you shouldn't tell anyone about the test topic before you receive the ads. Or with the WhatsApp app hinting Meta about your topics of interest.