Parts of the German school system and military have started using Matrix recently as well for its open source, secure infrastructure:
https://www.bwi.de/news-blog/news/artikel/kommunikation-in-covid-19-zeiten-bundeswehr-setzt-instant-messaging-ein

In other words, if you don't want some company, human or other middleman to have access to your communications, then using a foss, federated protocol like Matrix is the way to go. You can even run your own high-traffic homeserver with less than 1GB of RAM:
http://runhost.onmatrix.tech