Want to set up an old Mac running Mac OS X Lion? William Gallagher explains the hoops you need to jump through.
Your collection of old macOS installer disk images is now worthless, and Apple has changed where it hides downloadable copies.
Apple doesn’t want you to download old copies of macOS but it is possible.
Any old macOS you have won’t run anymore, because the security certificates on them expired then. However, any old macOS installer that you can download from Apple now will work.
What you want is a list of links to old macOS or Mac OS X versions, but Apple doesn’t want that to happen.
At present, you can still manage to get macOS Mojave, and High Sierra, if you follow these specific links to deep inside the App Store. For Sierra, El Capitan or Yosemite, Apple no longer provides links to the App Store.
Gallagher’s page has a bunch of useful links.