I am using the DeviceActivity framework to let the user track their activity (so also for non FamilySharing users). For tracking to cover multiple devices, does the app need to be installed/running on all devices or can the OS report activity to the app on one device? I haven't found a way to do that...
Your app needs to be installed and authorized for FamilyControls (either for a .individual or .child) on any device that you would like to report device activity. For monitoring device activity, you must ensure that the "Share Across Devices" switch in Screen Time settings is enabled on those devices.
If the app is installed on multiple users' devices, does the device activity framework allow the app to store the device activity data and compare it across users? For example, user A uses an app for 1 hour and user B uses the same app for 2 hours. I want to inform User B that they were on the app for 1 hour more than User A or .5 hours more than the average. is this possible?