I was playing with a Motorola G72 and noticed this feature by accident: double-tap on the back of the phone to trigger a custom action.
Here is a video showing this feature
This is not the same as double tapping the fingerprint scanner. This phone has a front-facing under-display scanner.
It’s very neat and handy, I hope other phones implement this too.
Update: See this comment for a link to an app that enables the feature on many phones.
Back when I had my Mi A1, I used to run a Pixel 2XL GSI ROM that enabled the same feature.
I used that to take a screenshot, and later, show the accessibility menu when my power button and volume buttons stopped working.
CC: @[email protected] who is the only person I know that still has their A1