As far as I know you need to keep the bootloader on the SD card, because the Rock 4C+ has no internal storage to store the bootloader and USB etc is initialiazed later, so you can not store the bootloader on an external medium.
As far as I know you need to keep the bootloader on the SD card, because the Rock 4C+ has no internal storage to store the bootloader and USB etc is initialiazed later, so you can not store the bootloader on an external medium.