Startup issues possibly startup.nsh in EFI shell

Question

I have a mini PC that always boots into Windows no matter what boot order is set in UEFI. I thought there was a startup script on ESP/EFI partition that was overwriting the boot order at every startup so I removed the ESP partition, created it again and recovered the boot configuration using Windows 10 installation media. But that did not change anything. The PC still boots Windows by default. To boot from a live USB I have to press F7 and then select the entry for the USB. I also tried installing Ubuntu as well as Phoenix OS but they only boot for the 1st time (using F7 again) and never boot after that. I read these pages: https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#UEFI_Shell

https://software.intel.com/en-us/articles/efi-shells-and-scripting

How to delete OS from boot menu

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Installation_Guide_x8664/s3-ia64-postinstall-startup.nsh.html

but 'bcfg' did not work (looks like my efi shell does not support the command) and neither did 'fs0 - edit startup.nsh' (it does open fs0 saying it is not mapped)

I also tried mounting ESP partition in Windows and explore what is there. I did not find any startup.nsh there. There are 3 directories: Microsoft, Boot and PhoenixOS. Boot and PhoenixOS contain bootia32.efi, Microsoft contains lots of files including the .efi ones.

I am looking for a way to get rid of any startup script and use UEFI boot menu instead and I was wondering if anyone could point me to a right direction. Any help will be greatly appreciated.

Updates:

NVRAM entry Boot0001 pointing to EFI/Microsoft/Boot/bootmgfw.efi being created on every startup. Does anyone have an idea on where such script is being stored and how to disable It?

Answer 1

It may be a buggy firmware as mentioned in here

Proposed solution is to

Hijack the Windows boot loader—Some buggy EFIs boot only the Windows boot loader, which is called EFI/Microsoft/Boot/bootmgfw.efi on the ESP. Thus, you may need to rename this boot loader to something else (I recommend moving it down one level, to EFI/Microsoft/bootmgfw.efi) and putting a copy of your preferred boot loader in its place. (Most distributions put a copy of GRUB in a subdirectory of EFI named after themselves, such as EFI/ubuntu for Ubuntu or EFI/fedora for Fedora.) Note that this solution is an ugly hack, and some users have reported that Windows will replace its boot loader, so it may not even work 100% of the time. It is, however, the only solution that works on some badly broken EFIs. Before attempting this solution, I recommend upgrading your firmware and re-registering your own boot loader with efibootmgr in Linux or bcdedit in Windows.