Possibly I am posting the duplicate question as already described in the post below.
How to get admin access to files for all user's OneDrive
We are running in to same issue. Can not access any users one drive with following api:
https://graph.microsoft.com/v1.0/users/{userPrincipalName}/drive/root/children
we have all the permissions in place and account used for authentication is Global Administrator.
Interestingly,as described in the article below, when we provide access from the Admin Portal on each users one drive, above api works well with the same set of permissions.
https://sharepointmaven.com/how-to-access-someone-elses-onedrive-account/
When we try the api below, States code is 200 but no data. https://graph.microsoft.com/v1.0/users/{useremail}/drives
Appreciate your help.