If you cloned a bootable Windows 10 drive onto that external drive, then you just need to go into BIOS, disable Secure Boot and then set that External drive as the primary Boot Device.
That is great. There are writings about having to install Windows 10 ISO on the drive that makes the drive boot like a new install of Windows without any of the settings and programmes available.
Appreciate the answer.
I also read to make sure Legacy Support is the boot mode.