Secure Boot Violation on Cubi N ADL

[0_ever_mamb15f402ee]

I’ve bought a Cubi N ADL and would like to install Proxmox/Linux. When I try to boot, I get a “Secure Boot Violation” error.
I can’t figure out how disable secure boot. The menu is all greyed out. I can't unselect UEFI as well.
I’ve tried:

• Setting user and admin passwords
• Disabling fast boot
• Setting USB key to the first boot option

Nothing will let me access the Secure Boot menu.

 

[fauc]

1.Please modify "Secure Boot" to disable in security sheet in BIOS setup.
2.Please modify "Fast Boot" to disable in boot sheet in BIOS setup.

 

[0_ever_mamb15f402ee]

I could not access the secure boot menu.

I installed Ubuntu Server, and now I am able to access that menu to disable it.

If someone else encounters this issue, it looks like the solution is to install an OS that is signed with existing keys, then you can disable secure boot.