GarageBand 10.4.12
Compress a project in GarageBand on Mac
You can copy your projects to a hard drive or other storage device, or upload them to the internet to share them with other GarageBand users.
GarageBand saves projects in a file package that’s compatible with Apple services and storage devices formatted for Apple operating systems. To ensure that your project package opens correctly on a non-Apple device or internet service, you must compress the GarageBand project package before copying or uploading it.
Select the package in the Finder and choose File > Compress (or Command-click the file and choose Compress).
Note: If you’re using compression software from a developer other than Apple, refer to its user guide for instructions.