Metadata (who you speak to, how often, etc.) are NOT encrypted (and subject of personalization, marketing, improving app performance etc.).

https://ssd.eff.org/module/how-to-use-whatsapp

P.S. if shocked with this, also check your Google activity history

https://myactivity.google.com/myactivity?pli=1

-- For example, WhatsApp is also end-to-end encrypted, but collects more metadata than Signal.

https://ssd.eff.org/module/attending-protest

Why Metadata Matters https://ssd.eff.org/module/why-metadata-matters