Earlier quoted context omitted.
We would also need a definition of AGI that is provable or disprovable. We don’t even have a workable definition, never mind a machine.
We don’t need such a definition of general intelligence to conclude that biological humans have it, so I’m not sure why we’d such a definition for AGI.
I fully expect that, as our attempts at AGI become more and more sophisticated, there will be a long period where there are intensely polarizing arguments as to whether or not what we've built is AGI or not. This feels so obvious and self-evident to me that I can't imagine a world where we achieve anything approaching consensus on this quickly.
If we could come up with a widely-accepted definition of general intelligence, I think there'd be less argument, but it wouldn't preclude people from interpreting both the definition and its manifestation in different ways.