Pulling the external drive while Windows is running causes instant filesystem corruption. Unlike internal drives, Windows does not have a safe removal mechanism for the boot drive. Users must always shut down fully before disconnecting.
Once the process completes, restart your Mac. As it reboots, hold down the Option (Alt) key . You will see the boot manager screen. Select your external drive (it will appear as an "EFI Boot" or Windows drive icon) and press Enter. install bootcamp on external drive