Metadata and network traceability, you can easily create a communication graph. If you want a more private p2p application try berty, but Simplex is still superior from a privacy point of view.

GitHub

simplex-chat/docs/SIMPLEX.md at stable · simplex-chat/simplex-chat

SimpleX - the first messaging network operating without user identifiers of any kind - 100% private by design! iOS, Android and desktop apps 📱! ...