Unidentified Developer error message
In MacOS on Mojave or later, when an app fails to install because it hasn’t been notarized or is from an unidentified developer, it will appear in System Preferences > Security & Privacy, under the General tab. Click Open Anyway to confirm your intent to open or install the app.
The warning prompt reappears, and you can click Open.*
The app is now saved as an exception to your security settings, and you can open it in the future by double-clicking it, just as you can any authorized app.
If you’re prompted to open Finder: control-click the app in Finder, choose Open from the menu, and then click Open in the dialog that appears. Enter your admin name and password to open the app.