@Sokoban, Thanks for posting in Q&A.
From your description, I know you want to partition a disk using Autopilot.
Based on my research, Windows Autopilot is a collection of technologies used to set up and pre-configure new devices, getting them ready for productive use. Therefore, Intune Autopilot cannot partition a disk with C and D. However, when autopilot is done, you can use the built-in tool or third-part tool to do disk partition.
Here is a link with detailed information you can refer.
https://www.diskpart.com/articles/how-to-partition-c-drive-3889.html
Non-official, just for reference.
Hope this can be helpful.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.