My XPS 8950 desktop comes with Windows 11 but I want to install Ubuntu 20.04 on it. I followed instructions from the official Ubuntu website and prepared a bootable USB stick with Rufus tool (I also tried other tools such as Dell's OS Recovery and belenaEtcher but of no avail).

I was able to boot Ubuntu from this USB on other Windows machines but it is not even listed as a boot option when I press F12 during the boot of my Dell desktop (Secure boot is disabled, but other options such as Legacy Boot, USB boot priority etc. cannot even be found in my BIOS menus).

I have seen a similar problem being reported recently XPS 8950, will not boot from Windows 11 USB - Dell Community but solutions offered there did not help me as I cannot even see my bootable USB with Ubuntu.