My MSI Z97 motherboard (updated to the latest bios) seems to regard all of my bootable devices - SSD, HD, DVD-RW, flash drives - as legacy only. Specifically, if I switch to "Windows 8/8.1/10 mode ...

How to convert MBR hard drive partitions to GPT To determine if you have UEFI on your PC you will have to access the system software of your particular motherboard.

Learn how to convert MBR to GPT disk without data loss in Windows 11/10, using Diskpart, Gptgen, or AOMEI Partition Assistant. MBR disks support only 4 partition tables.