I struggle hard with this topic. I feel like being here, perceiving the world. Yet, if I simulated every molecule of my body, the simulated me would seemingly "feel" the same things, think likewise.
It feels there is more to "me" than what would be of the _simulated_ me. On the other hand I see no way to prove so.
This gets into the concept of free will.
If you have free will, then it is your own conscious decisions that are affecting the universe, and not the universe affecting your conscious decisions.
In this scenario, you can't "simulate every molecule" of your body, because that simulation will have to include whether or not you decided to touch that hot stove. And that decision rested solely with you, in your mind.
If we do not have free will, and this whole thing is "on rails", then we are essentially watching an elaborate movie play out that we have no control over.
I think whether you think a perfect simulation of a person has subjective experiences depends on what you think the substrate of that subjectivity is. If you think of it as a computational property then you'll be inclined to say "no, that simulation is experiencing things". If you think it is some kind of fundamental property of the universe, like pan-psychism, then you'll think the simulation is 'missing' subjectivity. Nothing in there about free will in my thinking.
Maybe our brains, as an evolutionary strategy, have tricked us into believing that the universe is fundamentally knowable and that the brain is the only reliable knowledge machine.
How would you know it's not true?