How can I install a non-notarized application that is not in the App Store and not from a verified developer?
In macOS 10.14 and 10.15, 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 &amp; Privacy, under the General tab. Click Open Anyway to confirm your intent to open or install the app.

See Safely open apps on your Mac from Apple Support.