Tap the Back of Your Phone to Launch Shortcuts
First discovered in a beta version of iOS 14, this accessibility feature lets you tap on your iPhone’s back to trigger an action or shortcut. You can choose from various activities during the setup, including taking a screenshot, launching Siri, or more. To enable this back tap feature, you can go to Settings > Accessibility > Touch > Back Tap. You then can choose the number of taps you want to use and the actions you want to trigger.