You may see an error message "The specified disk is not convertible" while converting an MBR disk into GPT by using the Diskpart utility. According to the error message, the disk you want to convert from MBR into GPT is not convertible. To fix this error, you should know what an MBR partition style is and what a GPT partition style is. If you want to convert an MBR disc into a GPT, your BIOS should support the UEFI mode. This is because the GPT disks use Unified Extensible Firmware Interface (UEFI) BIOS mode.
If you are getting this error message, first check your system's BIOS mode. If it shows legacy mode, convert it into the UEFI mode. To know the BIOS mode, click on Windows Search and type System Information, then select the System Information app from the search results. In the System Information app, you will see your BIOS made on the right pane.