Cannot resize a large partition to create an additional one

Desktop from HP has four partitions on disk 1: System (360 MB FAT32), Windows 10 C (1.807 TB NTFS), WINRE (832 MB NTFS), and Recovery Image (11.46GB NTFS). Since C uses less than half the available space, I want to divide it into two partitions. However, the partition is yellow and marked as "unsupported" and Disk Management is not available in the bar across the top. Why can't I resize the partition?