DELL Vostro 5490 BIOS unlock request

Hello to everybody !
I'm attempting to install other OSs then Windows on my Dell Vostro 5490 but I get blocked with access denied.
There's no problem with installing different boot loader ( e.g. Clover or OpenCore ) on external USB stick EFI and booting them.
But launching any installer, from within Clover/OpenCore, of other OSs always fails with access denied.

So i booted into UEFI Shell to look out what's going on.
I can list all filesystems residing on EFI partitions and see the installer files on the USB too.

But trying go access the main partitions always fails with "Level2CommandsLib/Ls.c(527): Node info != ((void*)0)"


To me that looks like there're restrictions inside the BIOS that prevent accessing the filesystems and booting other than
Windows bootloaders.

I've been searching for weeks now for any solution without joy. Some days ago I stumbled over this site and did read as much as I
could find related to this matter. 
I would really appreciate if one you could help me to unblock my BIOS from this restrictions, if that is possible at all !
Willing to learn something too !!

Attached the BIOS.exe

  Vostro_5490_1.7.0.zip (Size: 9.78 MB / Downloads: 0)