Most new ASUS motherboards do not have the option to let users to turn off the UEFI secure boot.
The Secure Boot Enabled is always greyed out and unable to change that option. Yet, you do have the option to disable the secure boot by clearing secure boot keys.
This is reversible so no need to worry about breaking the warranty or damaging the BIOS.
BIOS’s Secure Boot menu should show Secure Boot state as enabled and Platform Key (PK) state as loaded
Here are the steps on how to disable the UEFI secure boot:
When your computer first starts, watch for the enter the Bios or setup message, normally F2 or Delete key but can vary for different manufacturers
Once in the bios, locate and go to the Secure Boot options which is normally under Boot
Make sure the OS Type is Windows UEFI
Select Key Management
Select Clear Secure Boot keys
You will have the option Install default Secure Boot keys to restore the default keys after you cleared the Secure Boot Keys
After you cleared the Secure Boot Keys, Secure Boot will be automatically be disabled.
You can set the OS Type to Other OS now
Now exit out of the bios and make sure you save changes if prompted
