What is actually inside such a DMG is unpredictable. It could be:
GarageBand 10.4 requires macOS 11 Big Sur or later. If you are on an older OS like Mojave or Catalina, the App Store may refuse to let you download the current version, leading users to hunt for older version installers. garageband 104 dmg
A: Yes. Copy GarageBand.app from /Applications to an external drive, then paste it into the /Applications folder on the second Mac. Launch it – if it complains about missing components, re-download the Sound Library. What is actually inside such a DMG is unpredictable