It just installs the installation application so that you can run the installer. Your web browser will download the Yosemite installer as a disk image named InstallOS.dmg or InstallMacOSX.dmg. This next step does not actually install the MacOS. Scroll down to the Yosemite link and click on it. The App Store will automatically check what MacOS you are running, and download an older, compatible version. An App store account with a historical purchase of GarageBand that you can click on to redownload and install a copy of GarageBand.In order to install a working version of GarageBand, you will need two things: WARNING, PROCEED AT YOUR OWN RISK, AND MAKE SURE YOU HAVE A BACKUP OF YOUR SYSTEM AND DATA After jumping through some hoops, I am happy to report everything works as it did before I made the mistake of upgrading my MacOS to High Sierra. The earliest version you can still download and install from Apple is Yosemite. There is a solution however, but you have to be willing to revert back to a previous version of MacOS. After fussing with Apple support for two days, the simple answer is 'It doesn't work'! I tried installing GarageBand from the App Store, but it just kept crashing. I made the mistake of doing a clean install of MacOS 10.13.6, which is High Sierra. I've seen a lot of posts with people having similar issues installing GarageBand on their older Macs.
