Matrix has many features which make it antagonistic to privacy. For example:

• Data duplication and permanence are the highest priority.
• E2EE is not enabled in all cases in all clients.
• Metadata, including the membership lists and responsibility lists within rooms, is preserved permanently and historically across all servers that host the room
• When you send a message (according to the reference Matrix implementation) you transfer ownership of your data to everyone else in the room.
• Data deletion is an inconvenient and difficult thing to achieve. For example, sensitive media remains even if you delete the message containing it. For another example, you will be rate limited if you attempt to delete many of your messages at once - and you must delete only one message at a time.
• Requesting account deletion via GDPR does not delete a single message you sent. It doesn’t delete much data at all, really; it just replaces your original username with an empty placeholder.