Review of which macOS versions you can download on Mojave & High Sierra depending on your Mac Version.
After all this testing, we know what can be download from the App Store. We also found out what can’t download. After performing multiple tests with each OS you can download any newer version, the current version but only 1 OS behind. You will get a mixture of “The requested version of macOS is not available” or “This version cannot be installed on this computer”