I understand the DMA interop thing quite well, and it is a private API. The matrix bridge does not use official interop as the Matrix foundation has given up on plans to do interop, as it requires geolocating (and then georestricting) their users.
The current, longstanding, matrix bridge requires you to have the WhatsApp app installed on your phone, with a working account.











Orion (WebKit), like a hardened version of safari for Linux and soon Windows