How do I upgrade from High Sierra to Mojave? The link to the app store gives a message that the install mac OS Mohave application is damaged and cannot be used to install mac OS

Hey there! I’d try the previous suggestions. If you’re still having troubles with that error message:

Delete the current “Install Mac OS Mojave” from your Applications folder, then download and run it again:

https://support.apple.com/en-us/HT210190

(The second link under section 4)

If none of those steps fixed it, I have seen the same installer work fine in safe boot on some Macs, so I’d try booting to same mode and opening the “Install Mac OS Mojave” again from Applications:

https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac

Ive seen that work particularly with Mojave for one reason or another.

If that were to also fail, (Hopefully not):

Id create a new administrator account in System Preferences > Users and Groups > (Unlock) “+”, restart, log into the new user then install it from there.

Also since you do already have High Sierra, you could boot to internet recovery, as the link provided previously, (Startup with Command Option R), then hit Reinstall Mac OS, which should install Catalina, (Note if no drive shows up, you may have to first go to Disk Utility while in recovery mode, select Macintosh HD (Usually) > File > Mount, (Or Unlock), then enter your admin password and try the reinstall again,

If all else fails, there could be corruption on the startup disk, which you can attempt to repair, but I’d try creating a bootable installer to do the job:

https://support.apple.com/en-us/HT201372

Hope one step works out! There are other options if not!

If your computer can run Mojave, then it can run Catalina which is the current version from the App Store. If you prefer Mojave, then you may use one of the following links:

macOS Mojave - Pick one or the other

https://itunes.apple.com/app/macos-mojave/id1398502828?mt=12

https://apps.apple.com/app/id1398502828?mt=12

When you get that message it is the App Store detecting a copy of the Install macOS Mojave.app

in your Applications folder.

Locate it, move it to the Trash, empty the Trash.

Connect your mac to your router via cable rather than WiFi.

Restart your mac, go back to the Mojave download page in the App Store.

It should now say Get or Download.

Another tip: There are a number of recent reports that FireFox is not working for macOS upgrades. Use Safari for the download.

Great work 😎.

R