Can't install Garageband on Catalina

Aha, that could be the problem because it counts as a unique app. (For what it's worth, for testing purposes I was still able to download v6.0.5 just yesterday, and it still works on High Sierra, probably even on Mojave. Yay, nostalgia! :)

Anyway…

In that case, just last night I was thinking of a hypothetical workaround:

What you could try is to ask a buddy with a Mac running Big Sur to lend it to you.

Then temporarily log into the App Store using your Apple ID and download GB "pro forma" on their Mac.

Then it should appear in your Purchased tab on your Mac, and you should be able to download v10.3.5.

But I can't test it because I don't have a Big Sur compatible Mac either.

I was eventually able to make GB6 (aka GB'11) run on Mojave by downloading the "GarageBand 11 Compatibility Sounds and Instruments" via Logic Pro X's Sound Library Manager. But I guess it would have also worked if I had replaced the GB's/Logic's Sound Library folders with symbolic links to one of the other partitions with a full installation already intact. (Because that's the whole "trick" how Logic's "Relocate Sound Library" command works. ;)

Nonetheless, GB6 then choked on Apple's preinstalled AU plugins on Mojave! D'oh! Its built-in AU Validator just hangs. I had to force quit GB6 again and again, until GB6 marked all plugins as incompatible.

Installing the lessons also fails. Obviously the custom built-in installer doesn't get any permission to run:

Installation of /var/folders/jt/ctnf15_170sb8btbc5ysfskc0000gn/C/com.apple.GarageBand/downloads.apple.com/static/gb/gb11bc/GarageBandBasicContent.pkg didFailWithError:Error Domain=NSOSStatusErrorDomain Code=-2147409654 "CSSMERR_TP_CERT_EXPIRED" UserInfo={SecTrustResult=5, NSLocalizedFailureReason=CSSMERR_TP_CERT_EXPIRED}

Which means: I should have looked at the Console before, ha!

https://downloads.apple.com/static/gb/gb11bc/GarageBandBasicContent.pkg

That's what's missing.

You can then run the standard Mojave installer to install it separately.

GB6 will then still report an AU validation error on launch and ask for the lessons download. Just click Cancel.

To remove the Lessons download prompt for good, you may need to open ~/Library/Preferences/com.apple.garageband.plist with a plist editor (use e.g. Prefs Editor or the Terminal if you know what you're doing) and remove the "downloadStarted", "numRetry", "pkgName" and "url" keys from the "DfPrefs_ActiveMentorDownloads" dictionary. (For those folks who don't understand what I'm talking about: better just leave it alone for now. :)

Other than that, GarageBand 6.0.5 works on Mojave.

Have fun!

Which GB version is it that was installed?

Should be v10.3.5 which is the latest available for High Sierra, Mojave and Catalina.

Tested just last night on a High Sierra partition, the download was totally smooth, including the complete Sound Library.

Lukas wrote:

v6.0.5 […], probably even on Mojave.

(Just for the record: Nope, download of GB v6 doesn't work for me on Mojave. That could be due to general App Store issues I was experiencing on Mojave in the past few weeks. I can launch an existing copy of GarageBand 6 from another partition, so essentially it would still be compatible. But it gives me an error while wanting to install the required Library files: however, that could be because my Mojave partition is running out of storage, and there's simply not enough space to complete the instalation.)

Lukas wrote:

Lukas wrote:

v6.0.5 […], probably even on Mojave.

(Just for the record: Nope, download of GB v6 doesn't work for me on Mojave. That could be due to general App Store issues I was experiencing on Mojave in the past few weeks. I can launch an existing copy of GarageBand 6 from another partition, so essentially it would still be compatible. But it gives me an error while wanting to install the required Library files: however, that could be because my Mojave partition is running out of storage, and there's simply not enough space to complete the instalation.)

GarageBand 6.0.5 is working well for me on Mojave, but cannot run on Catalina because of 32-bit frameworks. Reinstalling from the AppStore is occasionally working, but not always. But the AppStore is still showing the download in my purchases.

I am keeping two of my Macs running Mojave just to be able to use the older GarageBand version and Aperture.

GarageBand 6.0.5 is from 2015, the last version of Garageband '11. Garageband 10 is the direct successor to GarageBans 6.0.5. GB 6.0.5 offers quite a few features, that the newer GarageBand 10 does not support, for examples the Podcast feature or the Sound Effects instrument, automatic Ducking, it is easier to change the pitch of Audio Files. GarareBand 6.0.5 has more software instrument loops than GarageBand 10. What is missing in GarageBand 6.0.5 are smart instruments and arpeggiators. I am still using the older version a lot, at least to create my projects.

See also https://support.apple.com/en-us/HT205927 for more troubleshooting.

Glad to hear that!

Cheers