The message is Rhino can’t be opened because Apple cannot check it for malicious software"
While I am running a beta version of OS 10.15–first time I have encountered this. Anyone else?
You are running the macOS Catalina Beta.
Right-click the application and select Open. A different, but similar, dialog will appear where you can click Open.
If the right-click menu is not enabled, navigate to System Preferences > Mouse > Point & Click (tab) > Secondary click and make sure it is enabled.
Thank you! That worked.
You should only have to do this once. I will work on getting Rhinoceros.app notarized with Apple so that this does not happen in the future.