Screen Time for iPhone, iPad and iPod is not able to recognize individual apps being used. It knows when the device is being used and when it’s not, you’ll see this reflected in the App Log where it will show you how much time was spent on the device as a whole.
We would like to display the app log with all of the different apps used on there, but this a restriction of Apple’s platform and until they change their policy we can’t improve this feature.