Once it's done, unmount the USB drive (right-click and select Eject) from the desktop. Simply select the Windows ISO image that you downloaded earlier, select the external drives and Etcher will create a bootable Windows drive on it.

Boot Camp Assistant will create the bootable Windows 10 USB. Open the Etcher USB boot utility that you downloaded earlier and make sure your external hard drive that you want to install Windows on is connected.

Select the Windows 10 ISO image from Mac's internal storage and select Continue.

Select Continue, and check the option to Create a Windows 10 or later install disk.

Click on Choose a Windows 10 ISO file, and upload the Windows 10 ISO file you downloaded in the previous step. When the download completes, quit Boot Camp Assistant. Launch Boot Camp Assistant on your Mac, and click Continue.

From the menu bar at the top of your screen, choose Action > Download Windows Support Software, then choose your USB flash drive as the save destination. Go to Finder > Applications > Utilities and launch Boot Camp Assistant. Open Boot Camp Assistant, which is in the Utilities folder of your Applications folder.To create a bootable Windows disk using BootCamp: You will also need a 16GB USB disk, alongside the Windows ISO file for this method. Note: You can't use Boot Camp Assistant on Macs with Apple M1 chips. You can also choose to install additional Windows support software, which will be helpful if you are planning to use the bootable disk to install Windows on your Mac. This is an easy method and requires no additional software to be installed. If you have a Mac with an Intel processor, you can also use BootCamp Assistant to create a bootable Windows installation USB disk. Method 2: Create a Bootable USB Disk Using BootCamp Assistant

How to get windows 10 on mac bootcamp