Have just taken delivery of an Intel NUC8i5BEK, installed RAM & SSD.
A USB stick with:
$ dd if=~/Downloads/devuan_beowulf_3.0.0_i386_desktop-live.iso
of=/dev/sdb  bs=512k
looks good mounted on another host, but doesn't boot in the NUC.

On power-up or Ctl-Alt-Del, the NUC reads the USB twice (LED on the
stick flashes),
but then reports "A bootable device has not been detected."

I've gone into the BIOS, and in the Boot Order tab, hit Advanced, then
in
Boot Configuration tab set "Boot USB Devices First". F10 to save.
That gives a Boot Devices list below with a greyed out "Internal UEFI
Shell",
followed by "USB", then the others below that. Looks good, but
returning to the
adjacent Boot Priority tab shows:

UEFI Boot
Priority                            
Legacy Boot Priority
------------------------                            
---------------------------
UEFI Boot                             
Legacy Boot 
Boot Drive
Order                             Boot
Drive Order  "No Boot Drive"
UEFI LAN: PXE IP4 ...
UEFI LAN: PXE IP6 ...

and the Boot Order tab seen on entry to the BIOS shows the same.

From that I infer that legacy boot from USB is not a BIOS config
option,
and that the Boot Configuration tab setting isn't recognised in the
Boot Priority tab's UEFI column. (At least for display, since the USB
is
accessed twice during boot.)

Can anyone spread a sprinkle of enlightenment on this apparent
impasse?

Erik