basically.

even minimal metadata for example from signal contains

Message dates and times

Message senders and recipients (via phone number identifiers)

From these 2 pieces of information, its possible to build social graphs: who talked to who, and when they did it. Also, who’s in a group chat with who else.

https://github.com/dessalines/essays/blob/master/why_not_signal.md#why-not-signal

(worth to read in full)

sure, but also

„We kill people based on metadata.“ Michael Hayden, NSA