I know it said that the device activity report extension data cannot be extract but what about importing data to the report ?
Device Activity Report Extension import data to the report
How do apps like Opal and Jomo create groups/squad to see friends screentime data?
There's no supported way for you to import data to your device activity report with the APIs currently available. If you'd like us to consider adding the necessary functionality, please file an enhancement request using Feedback Assistant. Once you file the request, please post the FB number here. If you're not familiar with how to file enhancement requests, take a look at Bug Reporting: How and Why?
Rico WWDR - DTS - Software Engineer