Whatsapp can't read the message on their servers but they can read it at clients, otherwise they cannot display the messages for users. Likewise, Apple/Google can read them too because they have to in order to render the texts.
We know the app decrypts it to display it. But if the app decrypts it to send it to the parent company, then it is by definition not end to end encrypted anymore.
If the app decrypts it, analyzes it and sends information about the message to the parent company, then the same thing is happening. The parent company is reading the message, INSTEAD of E2E encrypting it. It doesn't matter whether that reading happens on device or on the company's servers. E2E means the company is not reading it.