If you find that the C or D Drive letter is missing from Explorer in Disk Management in Windows 11/10, maybe after an Update, try these solutions to resolve the issue.

Step-by-step instructions for assigning a specific drive letter to an external drive, SD card, or hard drive partition in Windows 10.

Open Windows Explorer, right-click on the USB drive with it's uniquely assigned letter, and select Create shortcut. It'll appear on your desktop. Right-click it and select Properties.

If the secondary hard drive isn't showing up in File Explorer, you can use these steps to resolve the issue on Windows 10.