I can’t understand why it doesn’t see external usb to download win7 on mac?

Question

Boot disk

Good afternoon!
I have an external drive toshiba 500gb I want to roll win7 on it and use it as an external boot drive for poppy pro.
I do not understand why it is not seen among the possible downloads? in the Mac axis itself, the disk is seen and can be written or read.
Tell me what could be the matter?

Answer 1

In security settings