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Mac gives an error about stages sync application being from "unidentified developer"
Mac requires developers to be "known" to install applications without a warning for security reasons. Today's Plan is not certified for this authentication however the application can still be installed following the steps below.
See this support article to install applications like Sync: https://support.apple.com/guide/mac-help/open-a-mac-app-from-an-unidentified-developer-mh40616/mac