This is not a logically valid argument. If AGI isn't possible for any of the reasons you suggest, then human cognition isn't possible either. And you're making numerous category mistakes ... an AGI can't be "incomputable" or "undecidable" or "NP hard". A problem that we put to an AGI might be NP hard, but neither AGIs nor humans need to solve the entire class of problems, only instances of them, and they don't have to solve them optimally. Thus salesmen are able to travel.
To quote ChatGPT on this:
"Could cognition be NP-hard? Strictly speaking, no—if human brains were literally solving NP-hard problems in their general form, we wouldn’t be able to think at all.
Does cognition involve NP-hard problems? Yes—in theory, many of the domains we reason about are NP-hard in the worst case.
What’s really happening? Human cognition relies on heuristics, approximations, and exploiting real-world regularities, so we almost never hit the formal “worst cases” that define NP-hardness."