- Insert a BLANK USB device into the Mac.
This process WILL erase all content on a USB, please make sure all files are moved off the USB before encrypting it, or there is not data on the USB.
- Open Disk Utility - On the desktop select Go menu, then select Utilities.

- In the Utilities folder, open Disk Utility.
This might be easiest to find while viewing in List format.

- Change Show Only Volumes to Show All Devices.

- On the right side, select the USB drive and then on the Erase tab.

- Change the Scheme to GUID Partition Map.

- Under Format, choose APFS (Case-Sensitive, Encrypted).

- A pop-up message will appear to confirm that the drive should be encrypted. Enter in a password for the USB drive.

- Select Erase.
Progress bar will appear. When the encryption is complete, the formatting window will re-appear but grayed out.
- Once the USB drive is encrypted, data can be copied back on to the drive or just start usage.
- The USB drive can be safely ejected at this time.
- The next time the UBS drive is plugged into a MAC, it will prompt for a password to be entered.
