For full-disk encryption of thumb drives and USB hard drives, you can use BitLocker To Go, which is designed for removable media. You still need a professional or enterprise version of Windows, but you don’t need a TPM to use BitLocker To Go.
All you have to do is plug in the device you want to encrypt, and then once again go to the BitLocker menu. At the bottom of the menu, you’ll see the BitLocker To Go section, where you can click Turn on BitLocker next to the device.