Symantec Encryption Desktop has a Drive Encryption component that has the ability to encrypt the boot drive, as well as removable\external hard drives. Windows platforms have full functionality of this feature and has no limitations.
Drive Encryption for macOS has some variable functionality when it comes to Drive Encryption or Full Disk Encryption of boot drives, or external drives.
macOS can read drives encrypted with Symantec Drive Encryption (PGP Heritage), however, it is no longer possible to encrypt boot drives with macOS and those can be done with Apple's native FileVault solution.
If external drives have been encrypted with Drive encryption (PGP), these can be read on Windows (all platforms) and macOS until macOS 10.12. Once the macOS has been upgraded to 10.12 or beyond, the Drive Encryption component is no longer expected to work. If you need to be able to view files on encrypted systems, do not upgrade beyond macOS 10.11.
You could copy all the data and put the files into a Virtual Disk, which is fully supported on both platforms, and these virtual drives can be copied to external USB drives.
For more information on Virtual Disk, see the following article:
If you need to be able of the enable Full Disk encryption on macOS 10.12 or beyond, you can use the FileVault encryption.
Symantec Endpoint Encryption and Symantec Encryption Management Server (PGP-Heritage) both support FileVault recovery management.
For information on Symantec Endpoint Encryption for FileVault, see the following articles:
213004 - Using a Personal Recovery Key to unlock a machine managed by the Symantec Endpoint Encryption FileVault Client
213006 - Using the SEE Helpdesk Web Portal to obtain the Personal Recovery Key for SEE FileVault clients
213002 - How to install and use the SEE FileVault client to enable encryption and manage Recovery Keys with the SEE Management Server
213010 - How to create an Institutional Recovery Key for Symantec Endpoint Encryption FileVault Recovery