A free app for Android, by flar2.

With this program, you may modify how the back and recents buttons on Samsung handsets’ capacitive keys behave. Additionally, it interacts with Button Mapper to give users of devices running Marshmallow or Nougat more control over the backlight and touch vibration for the back and recents buttons.  Installing this application fixes the problem with the back and recent keys not lighting up if long press actions are assigned, and it adds new settings to Button Mapper.

This may not function on all Samsung smartphones and is only for Samsung devices. There is no need for root.