Unable to find USB-C in Finder to download file to USB

You're welcome.

To be clear, USB-C describes the connection port on the computer and the matching plug and communication language of the port.

The usb-c device you are attempting to use will be an external drive of some sort, perhaps a flash drive or something larger that might be used for backups. Or it could be something else such as an optical drive, speakers or dock or hub.

Exactly what type of usb-c device are you trying to use here?

Is the device plugged directly into the computer, or is it plugged into a dock or hub?

Here is Apple's guidance for using external drives with the Mac:

Connect and use other storage devices with Mac - Apple Support

Make sure you have enable the Finder to show these things on the desktop and/or in the sidebar.

Go to Finder > Settings... to configure these items.

Is your usb drive formatted properly for the Mac? (Have you used this usb before?)