Format/Wipe an Encrypted G Drive Mobile USB

Disk Utility now defaults to a volume view. You need to put Disk Utility back into Device view so you can erase the whole physical drive. To do this click on "View" within Disk Utility and select "Show All Devices" so that the physical drive appears in the left pane of Disk Utility. Select the physical drive and erase it as GUID partition and MacOS Extended (Journaled).

You can try these steps:

Install El Capitan or Later from Scratch

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility from the Utility Menu and click on the Continue button.
3. When Disk Utility loads select the drive (out-dented entry, usually model info and size) from the Device list.
4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
5. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
6. Click on the Apply button, then wait for the Done button to activate and click on it.
7. Quit Disk Utility and return to the Utility Menu.

This should create an empty drive. If you did not provide a name, then it is named "Untitled". I'm not positive this will work on an encrypted drive if you don't know the password. Since formatting the entire drive erases all of the data, it should not be a security risk. It may just work.