Gigabyte Z370M-D3H: Don't see my bootable usb @ bios boot priority

ykg

Prominent
Feb 6, 2018
2
0
510
Hi,
Tried to boot from my bootable USB flash drive in order to install win 10.
I've entered the bios "section" of the bios setup menu but when trying to boot from this device,
I couldn't set it to be first at the boot priority option. It didn't appear there at all !! Only my SSD hard drive appeared.

eventually I've used the "Override boot priority" option in the save & exit screen and there, my USB flash drive did appear.

Can someone explain?
 

ykg

Prominent
Feb 6, 2018
2
0
510
It is bootable. I've eventually installed win10 using this USB.
The thing that I don't get is why it is not enabled on the boot priority list but it is on the boot override list