The transition between macOS versions often breaks software compatibility. GarageBand 10.3.5 was a pivotal release that bridged the gap between older Intel-based Macs and the early transition to macOS Big Sur.
You may need to right-click and select "Open" to bypass macOS security settings for non-App Store software. Garageband 10.3.5 Dmg
Once opened, GarageBand will prompt you to download the "Essential Content." Ensure you have a stable internet connection. Troubleshooting Common Issues The transition between macOS versions often breaks software