External disks are different for each platform:
MacOS does not encrypt external disks by default and will only enforce internal disk protection.
Windows requires all disks to be encrypted to have data written to them.
For instance, if you insert a USB drive into a Cal Poly Windows device it will require you to encrypt the device prior to writing any data to it. You can opt to not encrypt the device, but it will remain read-only.
Once an external device is encrypted, it is recommended to save your secure passphrase to LastPass for future retrieval.
To encrypt external devices on a Mac you will need to utilize Disk Utility.
Some devices may be allowed as an exception for external disks.
To acquire an exception, please create a ticket and each case will be reviewed by the Information Security Office.
The official recommendation for file sharing on campus is via Microsoft OneDrive
Resources
How does FileVault encryption work on a Mac?