I think someone in Sony has messed up, and failed to include the 21:9 aspect ratio in the standard camera setup, despite this aspect ratio being available in the Camera Pro app and (we now find) in WhatsApp, that I assume must use the camera API to obtain photos from the phone camera hardware. Unfortunately Sony will never admit they have a problem with any of their phones, but I am sure they are aware of this problem and will be sorting it out.