I tried shrinking the C volume on my Win10 machine using Disk Management and it said that it was shrinkable by about 199GB. I chose to shrink it by 100GB, got the
request is not supported message, but the volume ended up being apparently shrunk by 100GB. As you can see in the screenshot, the disk is now 139GB, but the Disk Management shows no unallocated space. If I try to shrink it again, it says that it is now shrinkable by 99GB.
The reason I am doing this is to install Linux in parallel to Win10, and when I tried to boot from USB, Linux also showed no unallocated space. I have tried using the MiniTool partition wizard, but it does not show me the option to shrink/split this particular volume.
Any ideas on how do I either get back the "missing" 100GB that Windows no longer recognises or actually get those 100GB to appear as unallocated space for Linux to be installed on?