I've successfully managed to present the duration using DeviceActivityReportExtension,
however, I need to show the user how much time is left for him to use the monitored apps (The user answers questions and gains screen time that he can then spend using Social apps).
Everywhere I've looked said it is impossible to access the actual time spent on app but only to use DeviceActivityReportExtension to present it, but the app 1Question does precisely what I'm trying to achieve successfully.