The file types to register the application as a default handler for.
If you set file associations, Windows can automatically launch your application when the user opens an associated file type.
If you register the application as a file type handle, then it also handles file activation events.
In the Editor, Unity displays this under File and Protocol Associations in UWP Player Settings. For information on Windows file type association, see Microsoft's documentation. Additional resources: WSASupportedFileType.