Q: Copying GB APP from one MAC to my other

Good morning sburech,

If you are using the same Apple ID for App Store purchases on both Macs, you can download the new version of Garageband again at no cost. See this article -

Mac App Store: Frequently Asked Questions (FAQ) - Apple Support

Specifically -

Can I use apps from the Mac App Store on more than one computer?

 

Apps from the Mac App Store may be used on any Macs that you own or control for your personal use.

Thanks for using Apple Support Communities.

Best,

Brett L