Our Big Bang "may have been"
a super-massive white hole event,
"so we are" a universe-within a universe.
You need to revise the "so we are" into "so maybe one might imagine we could be" in light of the "may have been" part.
But taken as granted, let's just say the big bang actually happens to have been what you describe.
The first thing that such a hypothesis would reveal is that in such a scenario, the big bang we consider to be as an event of origin and the beginning of "space/time" suddenly is not at all the beginning of anything. It is no longer the origin of the universe. Now, there was something prior to it.
Second, if we look upone the universe, as it exists today, we find many super-massive black holes. At this point it becomes clear, that there are likely to be, or to have been just as many super-massive white holes. All contemporary, and all distributed in a similar fashion.
If there's one, there's another somewhere else. Just like we see with galaxies, or exotic stars, or exoplanets. If there's one, there's another somewhere else. So too for white holes.
Thus, even if the big bang, which we see as evidence in the cosmic background radiation, remains the most recent grand-daddy and mother of all cosmic events in the past 20 billion years, it cannot be assumed to be unique in THIS unerverse, and in THIS space-time continuum.
We can only draw the conclusion that in this very universe, there may have been another super-massive white hole event, prior to even the big bang, just as transformative in the distribution of mass and energy, and not only that, there will be a similar cataclysmic white hole event in the future, perhaps beyond the era of humanity as we know it, whether we continue to reside in this solar system and galaxy or not.
So, multi-verses are not a necessary conclusion to draw from white hole events, because there's nothing stopping total creation and total destruction and then total recreation from occurring and reoccurring in the same universe we seem to be in right now, simulation or not.
It'd be convenient if ET's only lived in black holes, although perhaps a little lonely, too.
So no, because we haven’t had lasers for 3000 years yet, and the black holes we can create here on earth last for microseconds.
Getting information back about the success of the effort is... challenging.
We would need one at a pretty uncomfortably close distance to perform this experiment in acceptable time and without needing insanely large amounts of energy.
Makes me wonder how close the next known black hole is. The center of the milky way?
Predicted by some solutions to relativity.
They have not been observed yet but recent theories suggest that some burst of gamma rays may be markers.
Other theories suggest that the expulsion of matter from a white hole may occur very quickly, almost instantaneously, so unlike say a supernova you’d need to be looking at the right place and the right time to see it happen.
White hole mass may be behind a horizion that makes them dark = dark matter.
Our Big Bang may have been a super-massive white hole event, so we are a universe-within a universe.