Apple Loops Copyright
The license for GarageBand (accessible from About Garageband) states:


  H. GarageBand Features and Support. Except as otherwise provided, you
  may use the Apple and third party audio loop content ("Audio
  Content"), contained in or otherwise included with the Apple Software,
  on a royalty-free basis, to create your own original soundtracks for
  your video and audio projects. You may broadcast and/or distribute
  your own soundtracks that were created using the Audio Content,
  however, individual samples, sound ￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼ sets or audio loops
  may not be commercially or otherwise distributed on a standalone
  basis, nor may they be repackaged in whole or in part as audio
  samples, sound libraries, sound effects or music beds.


If you include these loops in a larger work (i.e. you mix them in and they don't simply stand alone as a single sound), then you can sell or re-distribute that work under the terms of your license to those sounds.  You cannot distribute the loops themselves on their own as you would then be reselling / repackaging the  Apple loops.

If you were to create a composition that contained solely a single Apple loop, and tried to distribute that, it would not be allowed by the license.


https://support.apple.com/en-us/HT201808