Until the last update, to add a new person to the group, it was necessary to re-create the conference.
A trifle, but nice
Although the change is small, it significantly simplifies group calls. Now you can add a new person to the conference simply by clicking the "Add contact" button and selecting the appropriate chat, at the same time, all filters and effects are saved. The new feature is already included in the latest update of Facebook Messenger for iOS and Android.