You say that the AU and Standalone builds succeed, but do they run? Can you load the resulting AU in a DAW, or launch the Standalone? If the AU and Standalone don’t work, this might indicate that the framework dependency isn’t being resolved correctly. The VST3 build failure would be caused by the juce_vst3_helper failing to load the plugin bundle.
Framework dependencies are discussed here:
You could try adding the rpath flag to the extra linker flags, as mentioned in the final post. This might allow the system to find the framework dependency.