The recommended method to convert these disks is to upgrade the operating system to Windows 10 first, then perform the MBR to GPT conversion. So 2k8 sounds like a no no even for an offline conversion.

Consequently, the GPT disk is becoming a critical component of Windows 11. It may be necessary to convert MBR to GPT initially if you are contemplating upgrading your Windows 10 PC to Windows 11.

This post explains what is MBR (Master Boot Record), GPT (GUID Partition Table) and which technology is better for your SSD.