gpt drives have what is called a protective MBR so old MBR utilities will see that it is formatted with gpt. It has one partition entry for the entire gpt drive.

You can install a grub boot loader to the protective MBR's boot area, if booting in BIOS mode with Ubuntu, but then you need a bios_grub partition.

Windows will not boot from a gpt partitioned drive with BIOS so it cannot use MBR.