Simulating physics from first principles is not “mimicking human behavior.”
Our "first principles" are knowledge, not a new universe. You're not absolutely re-creating the entirety of reality. You're making a model that is useful, something that is "good enough" that it will produce outputs that can be used to roughly predict the outcome of real processes.
You think an entire simulated human being, that acts exactly like a living person for the same underlying reasons, must be different - somehow
No matter how detailed your simulation is, it's still physically different. You're admitting this every time you call it a simulation. You can tell the difference between a simulation and the thing it's simulating.
This is dualism
No, because I'm saying that consciousness is a physical process. You're saying that it's a mathematical process and that the substrate doesn't matter. I'm saying the substrate is a physical thing, and that consciousness is a physical processes, and so different substrates enable different physical processes. I don't claim that consciousness comes from some Beyond, or from Heaven, or from God. I'm saying it's a physical process, and that a simulation is a different physical process, no matter how detailed.