This may be a totally useless experience from another Dell
computer, but ...
I was running an older Fedora on both a non-Dell desktop
and a Dell Vostro laptop. I decided to do a fresh reinstall
on the laptop. First, used the desktop to create an install
flash drive (F34). Forget if I used mediawriter or dd, but
should not matter.
The flash mounted fine on the desktop. Took it to the
laptop, again mounted fine under the old Fedora. Tried
to boot from the flash and could not see it at all no
matter what bios boot options I tried.
Returned to the desktop and there was no problem booting
from the flash drive. But no success on the laptop until...
I recalled a brief message "Press F12 to ..." So brief I
had to <ctrl><alt><del> several times to get the rest that
said something like "select boot device".
When I next rebooted and pressed F12, it gave a menu that
included USB legacy boot, USB secure boot, and my hard drive.
Maybe the new Dell bios at your client needs something like
that to USB boot.
--
Jon H. LaBadie jonfu(a)jgcomp.com