Tap, Tap is an app that lets you use gestural shortcuts by tapping the back of your smartphone, so long as the model you have allows it. This feature was first implemented in Android 11 (on smartphones with ARMv8 architecture only).
With this app, you can use gestural shortcuts on the back of your smartphone to open apps, change settings, go home, go back, take screenshots, turn on the flashlight, and more. From the options menu, you can set up various 'gates' that block shortcuts in certain circumstances. For example, you can block all back-of-smartphone shortcuts when you're taking a call or have a specific app open.
Tap, Tap is an interesting app to try if you have a compatible smartphone, as it gives you an additional layer of customization to play around with, further streamlining actions you take on a daily basis.