Try this:
From the Windows boot media, his Shift+F10 to bring up the command prompt. Then do the following:
…
Even this (SodaStream’s comment #47) didn’t work. I have a Windows To Go (“WTG”) bootable USB with Windows 10 on it. I resized its UEFI partition to 240 megabytes. That didn’t work. Later comments made me realize that the issue might be with the primary disk’s UEFI partition. So I then followed SodaStream’s instructions while within the WTG environment and that didn’t work either. My main drive’s UEFI partition is 512M in size and is almost entirely free.
Now, I know that the installer is attempting to do something with that partition because after it gives the usual “your BIOS doesn’t support secure flash” error, the letter assignment is removed (and the drive is no longer accessible through that letter until I assign it again). The partition stops showing up in the list of available mapped drives.
I have tried everything short of buying a new NVME disk just for the purpose of installing Windows onto it so that I can update the BIOS. It simply should not be necessary to go to such lengths just to update the BIOS.
What in the world is going on here??? I’m pulling my hair out over this.
I’m using Ubuntu Unity (https://ubuntuunity.org) version 21.04. My NVME SSD is 1 TB in size.
I fully expect the standard Ubuntu installer will create its UEFI partition in the same way that Ubuntu Unity did, so I shouldn’t be unique here in this. My system is a batch 6 system that came with BIOS 3.06.