Seems to be the protocol.
Data sent on a potential regular basis based on a common web/desktop+smartphone usage even with a self-hosted client and Homeserver:
The Matrix ID of users, usually including their username. Email addresses, phone numbers of the user and their contacts. Associations of Email, phone numbers with Matrix IDs. Usage patterns of the user. IP address of the user, which can give more or less precise geographical location information. The user's devices and system information. The other servers that users talks to. Room IDs, potentially identifying the Direct chat ones and the other user/server.