A big Thanks to WindowsCentral.Com for the following information
To convert a drive from MBR to GPT on Windows 10, use these steps:
Search for Command Prompt, right-click the top result, and select the Run as administrator option.
Type the following command to validate the drive and press Enter: mbr2gpt /validate /allowFullOS
Type the following command to convert the drive to GPT and press Enter: mbr2gpt /convert /allowFullOS Once you complete the steps, the command-line tool will reduce the size of the primary partition and change it from MBR to GPT. MBR2GPT return codes
If the processes are completed successfully, the return code would be "0," but if the process fails, you may see one of the 11 error codes: Return codeDescription
1 User cancelled the conversion.
2 Internal error.
3 Initialization error. 4 Invalid command-line parameters. 5 Error on the geometry and layout of the selected disk. 6 One or more volumes on the disk are encrypted. 7 Geometry and layout of the disk don't meet requirements. 8 Error while creating the EFI system partition. 9 Error installing boot files. 10 Error while applying GPT layout. 100 Successful conversion, but some boot configuration data didn't restore.MBR2GPT important details
You can use the MBR2GPT tool on a traditional hard drive (HDD), solid-state drive (SSD), or an M.2 drive with virtually any version of Windows 10, but you must run the tool from a Windows 10 (version 1703 or later) installation.
When dealing with a drive using file encryption with BitLocker, you must first suspend the encryption before following the outlined instructions. While MBR-style drives can have up to four primary partitions, the drive you want to convert can't have more than three partitions because one additional allocation is required to create the UEFI partition. Finally, Microsoft designed the tool to convert drives running Windows 8.1, 7, or from an older version, but you can always upgrade the installation to the latest release of Windows 10 and then use the tool to convert from MBR to GPT.
How to change the firmware mode from BIOS to UEFI
After converting the drive to the GPT style, the computer will no longer start until you change the firmware type from BIOS to UEFI in the motherboard. Typically, this process requires hitting one of the function keys (F1, F2, F3, F10, or F12), Esc, or Delete key as soon as you start the device. However, since these options are always different, it's best to check your device manufacturer's support website for more specific details. On the firmware interface, find the "Boot" menu, enable the UEFI option, save the changes, and then the computer should start normally. Also, if you plan to upgrade the device to Windows 11 while in the UEFI settings, open the boot or security settings page, make sure to enable the "Secure Boot" option, and exit the firmware saving the changes. Check GPT partition styleTo confirm the device is using a GPT partition style, use these steps:
Search for Disk Management and click the top result to open the app.
Right-click the main drive and select the Properties option. Source: Windows Central
Click on the Volumes tab.
Under the "Partition style" field, the information should now read GUID Partition Table (GPT). Source: Windows Central
Check UEFI firmwareTo confirm the computer is in UEFI mode and Secure Boot is turned on, use these steps:
Search for msinfo32 and click the top result to open the System Information app.
Click on System Summary on the left pane.
Check the "BIOS Mode," which now should read UEFI. Source: Windows Central
Check the "Secure Boot State" information, which now should read On.
Once you complete the steps, if the System Information displays the mode as "UEFI," you have successfully switched the firmware type. After you complete the steps, if the partition is running using the correct partition style, you only need to check whether the device uses the UEFI firmware mode.