can't install iCloud Drive on iPhone 7
Typically, this is restricted via MDM profiles. To check, open the settings app and inspect your profiles.


Tap settings app
Tap general
Scroll content up if needed to see Profile (above Regulatory and below VPN)
Tap in to each profile you have and inspect what it restricts.


If you have no profiles, I believe the profile entry is hidden so you might need to look for another answer if you don’t have a profile restricting this.