Hi Bradley, This is Ramesh.
Your USB flash disk is using the drive letter D. Ejecting it should free up that drive letter, which you can use for your secondary hard drive.
Regarding partitioning, you can create as many partitions on that drive as you want, depending on how you want to organize your files. For instance, you may maintain a separate partition for Music files. Or even a single partition is fine.
The following guide can help.
How to create partition on Windows 11:
https://pureinfotech.com/create-partition-windo...
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