To support system acceleration with Intel Optane memory, the drive to be accelerated must contain at least 5 MB of continuous unallocated space at the end of the drive. Intel Optane memory needs this space to store configuration information to successfully pair the drive with the memory module. See the attached image for example. The 100 MB in the end of your C drive is allocated partition. In order to make it "unallocate", right click on it and then click on "Delete volume.."
In addition the drive should have GPT partition (rather than MBR ) Only Windows 10 64 bit 1803 (or later) is supported.
I don't know yet if your Windows is 64bit version. Left click on start and then open System > About. See the attached image.
I understand that you changed the partition type to GPT using MBT2GPT utility? If you did this it is OK. However what is this 100 MB allocated partition in the end of your drive? Is this an OEM partition? You need move it to left. You need unallocated partition in the end of your drive.