error while trying to install macOS Monterey
Why I cannot install macOS Monterey? When trying the I get this message: "This copy of the Install macOS Monterey application is damaged, and can't be used to install macOS.
MacBook Air 13″, macOS 10.14
It is telling you that there is a Monterey installer already present in the /Applications folder. You should be able to delete it, and then, try updating again. You may also want to update after first booting up your Mac in Safe Mode.
Ref: How to use safe mode on your Mac - Apple Support