Deep inside the MIUI 12 beta code, XDA-Developers was able to unearth a back tap feature that was introduced in Apple's iOS 14 and is reportedly on its way to Google Pixel phones as well. But Xiaomi's implementation takes things one step further.
From the screenshots below, you can see that there's a triple-tap on the back in addition to the double-tap. The list of supported tasks has been expanded so you can open up the control center, notification shade, the default camera app or take a screenshot by double or triple-tapping on the phone's back.
Additionally, you can turn off the screen, close the current app, do a split-screen, or show the menu in the app that you are currently using. That's all pretty neat but it would take some time for the feature to be released to all Xiaomi devices set to receive the MIUI 12 and we don't know when's going to happen. It's a really cool feature, nonetheless.