This is interesting. I believe that we are agreed. A very effective simulation would have intelligent life in it believing that it was real. We cannot prove that we are or are not in a simulation. It is not sufficient to regard no proof of being in a simulation as proof of being real.

In a legal court case if there is insufficient evidence to produce a conviction then a 'not guilty' verdict must be given. But it is not proof of innocence, though for all practical purposes we have to regard the defendant as innocent. The defendant may or may not have actually committed the offence.

This characterizes my view of simulation. Since there is, as yet, no proof that we are in a simulation it is sensible to believe that we are not because to claim that we are in a simulation is by far the more exotic of the two answers and the burden of proof has to be on the folk who believe that we are.

Yes, you may be Truman of the Truman Show film with the difference that everyone / everything else is actually a simulation, an environment set up for you. I cannot prove otherwise because I cannot prove to you that I am real.

We are also bordering on the free will issue, another interesting topic. I feel obliged to say that we have free will.