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.
Samsung has this as well as triple tap under RegiStar via Good Lock, but it randomly just stops working. It was great at first, but now I don’t even try to use it because so often it just doesn’t work.