The Signal messenger and protocol.

Keep in mind that Matrix' protocol and backing corporation are antagonistic to the idea of encrypting or deleting private data, to the point of fighting in favor of never deleting your username or messages when explicitly requested.

The fact that they will occasionally encrypt some of the messages transferred across its protocol is practically anecdotal. For anything it actually does end to end encrypt, it will still retain the metadata with the same fervor as with all the other messages.