It is not strictly meaningful to ask "are we in a simulation" since there are copies of us both inside simulations and outside of them. However, if it is possible to demonstrate decision problems in which the optimal decision depends on whether the problem is nested in a simulation, then it is meaningful to ask how to make the decision.
If all the copies of you that exist in a simulation either exist in complex universes (compared to the universe in which you are not in a simulation) or very late in time (so that they are strongly affected by the temporal discount in the utility function), you should behave as if you are not in a simulation.
It is not strictly meaningful to ask "are we in a simulation" since there are copies of us both inside simulations and outside of them.
Take my usage to mean: "is our most outer copy in a simulation?"
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.