When I click in appstore https://apps.apple.com/us/app/macos-mojave/id1398502828?ls=1&mt=12 on button "open" it writes that This copy of application MacOS Mojave installer is corrupt and it's not possible to use it for installation. This is unique way which I found for official Mojave installation and it doesn't work. Do you have some help? My Mac runs on High Sierra in present, I don't want Catalina.
Thanks.
Mac mini, macOS 10.13
If the other two suggestions don't work for you try this. Go to System Preferences → Date & Time, untick the box next to 'Set date ..... automatically' and change the year date to 2019. It's not common for Mojave misbehave like this but is a common fix for systems from 10.10 onwards to change the year to a date closer to when it was released.
Don't forget to change the Date & Time back after the install has finished otherwise your internet won't work properly.
Delete whatever installer you have in your Applications folder and try to download it again.
When you download, use Safari, not FireFox. There are many reports of macOS system upgrade files failing to download with FireFox.
Mojave installer
