Does Whatsapp expose these messages via an API? If yes, then it seems like this is not only on Google.
If no: Are they reading data from raw UI widgets? Are they intercepting input controls? Are they intercepting network traffic? That seems unlikely, given its probably end to end encrypted and the decryption happens within the scope of the Whatsapp process.
Why not... they control the OS, it'd be trivial to add hooks to the "draw widget" command to intercept that it's about to draw a text widget for WhatsApp, and then ask it to log the text.
WhatsApp data is encrypted, however, the keys are on the device itself and accessible on Android. There are many third-party apps that support transferring WhatsApp data from one phone to another, and some even claim so between Android and iOS devices. As I understand, the chats are in some usual database format. So anyone having access to the device can read the data even without WhatsApp being there itself (as far as the data is there).
>When granted, an app with accessibility permission can:
Read screen content (including text and buttons in other apps)
Detect user interactions (like taps, swipes, or gestures)
Navigate between apps and the system UI
Monitor app launches and foreground/background changes
Access and control other apps indirectly
Perform gestures or clicks on behalf of the use