Controlling who can use CloudFiler
You can control who has access to CloudFiler via the Microsoft 365 admin center.
In a browser, navigate to the Microsoft 365 admin center portal https://admin.cloud.microsoft/ (Link opens in a new window)

In the search field at the top type Integrated Apps and hit return. If it doesn't appear you should find it under Settings.

Select CloudFiler from the list and then in the box that appears on the right, select Edit users

You can then add people by name or by group.
WARNING: It can take up to 24 hours or more for Microsoft's servers to register any change. This applies to both enabling and removing the Add-in.