If it is possible that to make a simulation which matches our experience, then it is likely possible to make an unbounded number of such simulations. Thus, if such simulations are possible, it is vanishingly unlikely that we are executing directly on the underlying substrate.

If it is not possible, then, well, it's not.

So to a good approximation, the question "do you believe it is more likely than not that we are living in a simulation?" is equivalent to the question "do you believe that a simulation of the phenomenon you have observed is possible?"

And... well, sure, there's not a strong reason to think it's /impossible/, based on the evidence available to us. So, yeah, more likely than not.

Another way of phrasing this: Do you think it's more likely than not that there's some physical law, as yet discovered, that makes high fidelity simulation impossible? Such a law is certainly imaginable (limits on information density, magical-ness of souls, whatever); but if you don't have a reason to believe such a law is likely, then you probably believe we are more likely than not in a simulation.