Signal can’t see who is texting who. They can’t see which groups you are part of. Those information are end to end encrypted, same as your chats itself, your profile picture, your stories, etc.
This is completely false. They can absolutely see who is texting who, in fact they need it to be able to route messages. They have message timestamps, and phone numbers stored in their database.
Question, why do you “trust” signal? You can’t see what code their centralized server is running, unlike matrix which you can self-host and build from source. You don’t have to “trust” matrix, you can verify it for yourself.