Are you trying to shrink the OS partition from inside the OS?
For this sort of thing, I'd boot from a Linux USB and use gparted to resize it.
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Are you trying to shrink the OS partition from inside the OS?
For this sort of thing, I'd boot from a Linux USB and use gparted to resize it.
I’m disabled BitLocker, and then the free version of Minitool Partition was able to resize the partition as a reboot action. On to dual boot install!
Consider adding this to the main post and editing your title to say "[Solved]..."
[Solution] I disabled BitLocker within Windows, then installed MiniTool Partition Wizard Free 12.8. Using MiniTool, (now that the partition was showing as NTFS and not BitLocker), it allowed me to set a new smaller size, with a prompt to reboot (cannot modify the C: partition while in use).
The system rebooted and before Windows loaded, the partition app did it's thing. Windows then started normally with the smaller partition and no errors.