Here are descriptions of the more relevant changes in 21.0
It is possible to create groups to exchange messages with multiple contacts at the same time. The messages are always encrypted end-to-end.
The creator of the group becomes the administrator who can add new users or get users out of the group. Members of the group may leave the group on their own.
The Privatewave client for iOS is now integrated with Apple libraries to manage incoming calls. You no longer need to unlock your phone via Touchid or Faceid but simply swipe it like a normal call.
To increase security the PIN to unlock the application is now 6 digits long.
It is possible to reply to a message by quoting the text of the message to which it responds.
You can share your location as a secure message attachment
It is possible to delete a message already sent in the chat. Other users will no longer see the content of the message removed but a "Message removed" placeholder.
Support to new dark theme on iOS and Android 10.