When you boot a standard Linux or Windows virtual machine, VirtualBox uses a FAT32 EFI System Partition (ESP). The UEFI firmware reads EFI/BOOT/BOOTX64.efi directly from FAT32 seamlessly. macOS, however, complicates this process:
This is a known VirtualBox bug with memory mapping. vboxhfs.efi successfully loaded the bootloader, but the bootloader cannot find the root filesystem. Fix: In VirtualBox settings, disable "Enable EFI" (temporarily), boot once with legacy BIOS, then re-enable EFI. Alternatively, increase RAM to 4096MB or more. vboxhfs.efi