I've expanded my Fusion on MACOS Monterey virtual hard drive on my Windows 10 VM to 1 TB and the size shows correctly in Settings but my C Drive is still showing 200GB with only 10 GB remaining. I must be doing something wrong. Please post a suggestion.
You also need to extend the disk partition of your disk (for example the C:\ drive) within the Windows guest OS.
See for example:
for more info.