We'd like to take this opportunity to wish you a Happy Holidays and a very Merry Christmas from all at Golf Monthly. Thank you for sharing your 2025 with us!
They are essentially two different things. GPT is a partition type (newer UEFI type applications), MBR would be the "comparison" partition type. Basically GPT is used in newer UEFI enabled systems. MBR is more legacy.
Dynamic disks can be used on both GPT and MBR partition types. So it's not really a case of the difference between them as they are different aspects of a disks set-up.
Edit to add: If this is for that external drive use then I would use MBR partition type to make it more universal and FAT32 as the formatting withing the partition.
And there is the drawback of using an internal hard drive for external purposes. From what I understand Shield will mount a drive in either exFAT or NTFS. Not sure how accurate that is, but it's a decent start point.