The UMich article contains a quote that I think argues that there is nothing “on the other side” of black holes that could be the birth of a new universe: “If cosmological coupling is confirmed, it would mean that black holes never entirely disconnect from our universe, that they continue to exert a major influence on the evolution of the universe into the distant future” Tarlé said.

That suggests to me that popular notion that black holes are an entry point to a wormhole leading to a new place would be unfounded.

No because we have tools that can measure those energy levels and we don't see "invisible things" with them.

For the second part I have no idea, but that would be a fun thing to discover, universes just feeding into each other.