It is used in a non-federated context as the underlying in a lot of places (NATO, Zoom, british Military, Grindr, Jisti…). Federated usage is mostly private chats that don't really want to advertise that they do use it. It is sad because public groups also just work, but I know clients are missing a few features that would improve usability/UX. Some people are working on that, cf https://movim.eu/ for instance.