When an application runs with elevated permissions the drag and drop functionality does not work.
When an icon is dragged over the application, usually the copy icon should appear instead the forbidden icon is shown .
The open option works fine however a file cannot be dropped in the application.
This behavior is related to the integrity level used in elevation process for the application, a component with a lower integrity level (drag and drop) by
default, is not allowed to interact with a component running at a higher
integrity level, when the process permissions are elevated to a higher
integrity level then the drag and drop functionality will be automatically disabled and will fail, this process is the User Interface Privilege Isolation (UIPI).
To avoid this behavior the when creating rules, the integrity level selected must be at least Medium (selecting the Integrity tab in the Edit Privilege Elevation Rule Wizard).
The rule must be saved to take effect in next group policy update process.