If you want to silent your device when capturing a screenshot or taking a photo, read this tutorial, it will introduce 4 options to turn off Camera shutter sound in iPhone/iPad.
Your device has a Ring/Silent switch, make sure it's set to silent mode.
Use the Volume Down button to toggle iPhone volume down to the mute mode.
This feature is incredibly useful when you want to take photos of people you don’t know. They also have volume buttons, and you can use these buttons to take pictures.
You can search for different apps on the Apple App Store and test the camera apps to see which app doesn’t make a camera shutter on your iPhone.
Best iPhone Camera apps
VSCO is a popular iPhone camera app, it is used in every situation to take photos or edit images. It's free to download from the App Store.
Camera+ is a great camera and image editing app combined. It costs $2.99 from the App Store. This is the first advanced camera app I ever used for the iPhone.