iMovie music for commercial use

You can use the GarageBand music for commercial use, but not the iMovie music. The licences are different.

Try to find the music you want in the GarageBand loops.

And create the soundtrack for your movie with GarageBand.

Only GarageBand has this liberal text in the licence: Using royalty-free loops in GarageBand with commercial work - Apple Support

"The GarageBand software license agreement says:

"GarageBand Software. 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 music compositions or audio projects. You may broadcast and/or distribute your own music compositions or audio projects that were created using the Audio Content, however, individual 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 effects or music beds."

So don't worry, you can make commercial music with GarageBand, you just can't distribute the loops as loops."