I wasn't talking about Einstein-Rosen bridges. In fact I was wary of using that analogy because I suspected, correctly, that it would be misunderstood.

It sounds like you are saying that any possible reality could only interacti with another one using Einstein-Rosen bridges. This is far too narrow a limiting of what is possible. If it's possible at all, regardless of likelihood, that reality could be a simulation, then anything you say about the Einstein-Rosen bridge is a property of the simulation, and not a limit on reality as a whole.