The stock versions of Windows 10 does not run from USB. Linux and other OSes might but Windows requires the expensive Windows Enterprise and for Education systems. Read https://en.wikipedia.org/wiki/Windows_To_Go
As to the Macbook booting Windows from USB you have too many hurdles in my opinion here.
There is a trick I used long ago to get at a dead OS on just the pulled HDD. It's complicated and I only share to get you the method but do not offer more.
What did I do? I used a tool to convert the drive into a Virtual Box appliance. https://www.howtogeek.com/213145/how-to%C2%A0convert-a-physical-windows-or-linux-pc-to-a-virtual-machine/ gives you a look at ways to get this done. There are other issues such as Windows will balk at the hardware changes but it did allow us access to the point we could move the necessary information into a new Virtual Box instance.
Hi, so my vaio laptop died on me recently, the fan doesn't run as the windows is going to show up. Anyway, I manage to make its HDD to an external one. I connect it to my other laptop, that is macbook early 2015 model(but is running both mac os and window 10-which I mostly use) The external hard drive showed up fine, but it's more like plugging an USB into my macbook. I want to make it bootable as I don't have much option with my original hard drive. Its storage is too low for me to perform any task like I did with by dead vaio laptop.
So tl;dr, I want my macbook to act like my dead laptop, booting my now' new';external hard drive. Is that possible?
Also, I've tried booting from bios, but I couldn't access bios screen since I got no UEIF firmware option .What can I do?

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