OK, first of all I can assure you that install.wim is in the Sources folder of the iso if it is an official download. The problem is that there isn't a folder called Cortana in the WindowsApp folder in the intall.wim Program Files. I tried extracting all of the folders in the Program Files of install.wim to WindowsApps on the disk drive and then ran the PowerShell command in admin mode. Some errors came up and it appears it didn't work correctly. My hunch is that MS has altered the contents of install.wim. For now this method doesn't work, so I suggest you follow Mr GRiM's advice if you want the native start menu to function properly.