It is the same issue the developers are tracking at https://github.com/arduino/arduino-create-agent/issues/637. Please see the latest official statement about the situation, which was made today:
https://github.com/arduino/arduino-create-agent/issues/637#issuecomment-981693114
Upon further investigation this is something we can't seem to be able to tackle unless InstallBuilder allows shell scripts to be executed.
There is a chain of trust which fails when launching an AppleScript invoking a Shell script.For now, users who get this issue, please run this command in the terminal after installing the Agent
sudo security add-trusted-cert -d -r trustRoot -k /Library/Keychains/System.keychain /Users/$(whoami)/Applications/ArduinoCreateAgent/ArduinoCreateAgent.app/Contents/MacOS/ca.cert.pem