I have the same problem on my iPhone 7 plus, but for me it started happening when I upgraded to iOS 14 (prior to that no problem). Now on iOS 14.1 and my Facetime / Whatsapp VIDEO calls crash instantly when the app tries to talk with the camera. VOICE calls work fine on Facetime and Whatsapp but video will crash the app instantly. Same happens with Skype. Facebook Messenger will not crash but shows a black screen ie the other person does not see me just sees black. I have reset the device completely and uninstalled WhatsApp and reinstalled, I have reset the network settings and also turned on the local access switch in settings. Nothing works cannot do any video calls at the moment.