Alternatively, use softwareupdate in Terminal (on macOS High Sierra or Mojave):
[Related search suggestions will be prepared.] Download Mac Os Mojave 10.14 6 Dmg
If the Mac App Store link fails, use a trusted Mac that once downloaded Mojave. Apple lets you re-download previous macOS versions from your tab in the App Store. Alternatively, use softwareupdate in Terminal (on macOS High