Downloaded an image, want to install an older macOS and you get this message? “Install MacOS Application is Damaged, Can’t be Used to Install MacOS”
The problem is most probably related to an old expired certificate.
To install macOS without this problem you can try the following:
- Disconnect all Internet connection to your Mac. Disable WiFi, unplug ethernet cable, docking, etc.
- Open terminal from Tools-Terminal. Change your systems date to a year before (or two).
- Try again.
It worked for me, hope it worked for you.