There is no option in the settings to turn off screenshot sound on iPhone. To do this, you can turn on silent switch or manually lower the sound option slider. Or use the Live Photo feature or take a photo while recording a video.
You can add AirPods charge widgets on your iPhone, iPad and Apple Watch. On Mac, there is no built-in option to add a charge widget. However, you can check the charge of AirPods and case through Menu Bar or System Preferences.
To find out if you need a firmware update, first check what firmware version is installed on your AirPods. On your iPhone, you need to open Settings and go to Bluetooth. On a Mac, the steps will be different depending on the macOS installed.
You can change notifications sound on your iPhone for default apps and actions. And you can also use iPhone settings to change sound for a specific app notifications, but that works not for every third-party app.