garageband Jam pack

Looks like there may be 150 things that affect that...

https://support.apple.com/downloads/garageband_update

Also...

https://discussions.apple.com/thread/8562051

My Jam Packs are still working, but apple is no longer selling the Jam Packs.

Do you still have the old, original installer DVDs?

Running the installers has been a problem since the upgrade to MacOS X 10.7 Lion killed Rosetta, because at least one on Jam Pack installers uses PowerPC code.

My solution to installing the JamPacks on new systems has been to buy MainStage from the Appstore. Both MainStage 2 and 3 contain all five JamPacks and make it easy to install them.

Once you installed MainStage 3, launch it and use the command "MainStage 3 > Sound Library > Sound Library Manager".

In the dialog select the JamPacks you want to use. Once they have been installed by MainStage and restart the Mac. You will see the jam Pack instruments in GarageBand 10 in the "Legacy" section of the sound library.

If you are migrating from an older Mac, where the Jam Packs are already installed, you could migrate them from the older Mac, if you set up the new Mac from the old Mac.