"This copy of the Install macOS High Sierra.app application is damaged, and can‘t be used to install macOS."
Apple's October 2019 link to download 10.13 High Sierra failed:
https://itunes.apple.com/us/app/macos-high-sierra/id1246284741?ls=1&mt=12
Got this popup:
"This copy of the Install macOS High Sierra.app application is damaged, and can‘t be used to install macOS."
MacBook Air