I have a bricked Dell tablet that doesn't boot and also a has locked bootloader (Secure Boot: Enable). I've made a full partition dd backup, but now I cannot flash it via fastboot supposedly because of the locked bootloader. I obtained root before making the backup and so this backup seems to be unsigned, as they said me here.
I tried to unlock via
fastboot oem unlock but it throws
FAILED (remote: unknown OEM command)
fastboot flashing unlock doesn't work as well.
This tablet has BIOS but it doesn't have option for disabling Secure Boot.
I found this instruction how to disable Secure Boot, but I wasn't able to fulfill it, 'cause I got flash_cmds error while flashing osloader.
Is there any chance to unlock bootloader or fix it some other way?