You can disable the shutter sound for all external cameras in the settings of the app. As per regulations, you can't disable the shutter sound for the built-in camera. If you need to disable the shutter sound for the built-in camera, i.e. for a timelapse recording, use the mute switch on the site of your device. If your device does not have a mute switch, open the control center and tap the 'Silent Mode' symbol.