First get a Developer ID signing key from apple. You can get this through xcode if you're subscribed to their developer service.
Once you have a Developer ID in your keychain; you need to add a per-app password for notarytool
.
To do so go to your Apple account settings and add a new per-app-password; copy the password.
Run xcrun notarytool store-credentials --password "<INSERT PER-APP-PASSWORD HERE>" "notarytool"
.
After this you can add sign.sh and entitlements.plist to the outside of your Unity application, first time run chmod +x sign.sh
.
You can then run ./sign.sh <name of app>.app
and wait.