Creating a bootable USB
One way get a current 100% genuine Windows 10 USB flash drive would be to run the MediaCreationTool18.09.exe application. This would require Windows. To get Windows you would have to download the latest Windows 10 ISO file and install Windows a virtual machine. Oracle offers A free virtual machine called VirtualBox. I believe you will need to instal the Oracle VM VirtualBox Extension Pack after installing VirtualBox.

The link to get the MediaCreationTool18.09.exe application is given here. However, you can not access this link from macOS. You will need to click on the link while running a web browser under Windows. See this answer for an explanation.

A possible alternative would be to MS-DOS (FAT) format (using the Master Boot Record Scheme) a flash drive and copy all the files from the Windows 10 April 2018 Update ISO file to the flash drive. If you use the Windows 10 October 2018 Update ISO file, then the flash drive will need to be ExFAT formatted. These ISO files can be downloaded from this website.


  Note: The official Windows 10 USB installer is FAT32 formatted. There is no guarantee your PC can boot from a ExFAT formatted USB flash drive.