Other than your disbelief (which is understandable- indeed it’d hard to imagine), I didn’t find any deep arguments why AGI can’t “somehow” happen. How humans with their intelligence and self awareness evolved from non life (well, at some point super simple single cell organisms) is even more incredible. That computers will at some point posses so much data - in fact the entirety of data and knowledge ever accumulated- that somehow in its electrical impulses a new type of consciousness will be born - its far fetched but not inconceivable