Without some sort of technology that renders them truly immune to the "dangerous" space-time world, they won't be able to ignore it, because if their sun burps they all die if their simulators get destroyed. Even if they "all" happily charge into simulated bliss, a residual caretaking system should be visible as it performs the necessary cosmic-scale engineering to ensure that the simulated ones don't get wiped out by a cosmological crisis, such as a supernova. Further, any such society will still end up wanting more and more energy, so we ought to be seeing Dyson shells or something pop up, in the continuing absence of any apparently way of converting mass directly into energy.

We don't see any of these things. And the amount of "space" left in physics for some sort of true escape hatch that might let us escape fully into an impregnable universe of our own devising or something keeps going down and down.

I consider the lack of cosmic-scale engineering to be a much bigger problem than mere inability to detect signals. A lot of it isn't even that "hard" per se, because what's impossible on the year or century scale becomes feasible with only very realistic projections of what self-replicating technology can do if you can put in millions of years of continuous effort. And a lot of this stuff would both be visible, and essentially necessary; if life is so inevitable and intelligent civilizations so likely, quite a few of them will find themselves dangerously close to an incipient supernova on an uncomfortable time frame, and they ought to be doing things about that. Very visible things. It's just too perfectly quiet out there.