In your case, you can simply put it in traditional mode. UEFI is the only one that exists instead of BIOS boot. If there is more than one, only ESP on HDD 0 will take effect. The principle of UEFI is to read the boot file in the ESP partition of HDD 0. If HDD 0 has no ESP partition, some motherboards will try to read the ESP of HDD 1, and a few brand machines may only read the main disk. If the main disk has no ESP partition and startup file, the system will not start.