After the Tchap project based on Matrix, the French Prime Minister asks anyone in the gouvernement to use Olvid, the only app validated by the ANSSI, with metadata encryption and no centralised architecture nor contacts discovery. But only the front-ends are open source, not the back-end.
I can understand the WhatsApp part, its a closed source app but it makes no sense to ban an open source app bc of security concerns, just order a study of the source code to validate it
A far better reason not to use WhatsApp is that it is run by Facebook. It was also a primary vector for Pegasus.