Managed object vs. Native object
What is difference between managed and native mode in UWP projects?
And what is means:
This is because the fileList is not a managed object, and by default the Debugger type for a UWP project is "Managed Only". So you can't inspect it while debugging. You can try to change the Debugger type to "Mixed (Managed and Native)" like in this screenshot for inspecting.
from this post?
Managed Only means that only .NET code is debugged and that native C/C++ code is ignored. This is the default settings for C# and VB apps. You will find more information in the docs.
The actual implementation of the WinRT classes that your UWP app uses under the hood are implemented in an unmanaged language. The "translation" between the unmanaged and managed world is taken care of for you by the compiler and the projections that are built-in into each supported programming language.