Dowload icon is grey after reset due to restrictions, but screen time is off

My sons iPhone SE (12) had to have a factory reset.

iPhone is now clean and starts up again. We logged in on iCloud again

However ... Whatsapp and a few other apps can no longer be installed. I tried from the app store and from the the list of purchases. Apps are visible but the download icon is greyed out and there is a text saying that : "The app cannot be downloaded due to restrictions set for this device"

Who can help me? what restrictions are there and how can I turn them off?

It used to be working!

I already tried: turning Screen time off (and on, and off) again and to put back a backup (no backup available....)

device:

iPhone 5SE, iOS14

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