If Fast boot is enable, boot from Network / Optical / Removable devices and RAID configuration will be disabled. Also, video and USB devices (keyboards and drives) will not be available until after OS boot.
Removing the BIOS configuration jumper on the NUC allows you to update the BIOS and clear passwords only. The options to reset BIOS settings are 1) Pressing F9 from BIOS and 2) BIOS update.
If Fast Boot is enable and you need Boot Display Options (F2,F7,F10,F5); turn the NUC on, as soon as you are in the OS, unplug the power cord from the NUC then; plug it and turn the NUC on again the options will be available.
I think I've solved the issue.
If I press the F9 key as the NUC boots with a bootable USB device inserted, a different text menu comes up, giving the option to boot from the USB device or to continue booting.
When I choose the USB device it works.
So far so good.
Thank you for your feedback.