Under "How We Work With Other Meta Companies" in the privacy policy describes a usage almost identical to what the parent suggests:
> improving their services and your experiences using them, such as making suggestions for you (for example, of friends or group connections, or of interesting content), personalizing features and content, helping you complete purchases and transactions, and showing relevant offers and ads across the Meta Company Products;
> improving their services and your experiences using them, such as making suggestions for you (for example, of friends or group connections, or of interesting content), personalizing features and content, helping you complete purchases and transactions, and showing relevant offers and ads across the Meta Company Products;
https://www.whatsapp.com/legal/privacy-policy