If you need to grant a user or group standing access to a user's personal sites, you may want to consider assigning a secondary site collection admin. To set a secondary site collection owner globally, follow these steps:

1. Navigate to the SharePoint admin center Classic Features administration center (https://admin.microsoft.com | Admin centers | SharePoint | Classic Features).
2. Launch the User Profile Service application from the classic SharePoint admin page by selecting User profiles.

3. Under My Site Settings, select Setup My Sites.
4. Scroll down to My Site Secondary Admin.
5. Ensure the Enable My Site secondary admin box is selected. Then, add a username or security group through the user picker:

6. Scroll to the bottom of the page and click OK.

This change only affects OneDrive for Business sites that are provisioned going forward. It does not impact existing sites.