Indeed if universes are born in black holes then the heavy elements are a biproduct of the process and that explains why the universe is so fine-tuned for life.
Science actually knows how that happens, and it’s not in black holes. In the beginning (well, after the beginning, but we’ll start here), there was hydrogen. Gravity caused this hydrogen to coalesce into clouds. These clouds coalesced into smaller clouds. These smaller clouds coalesced into denser and denser spheres of matter. At a certain point many of these spheres were so dense that the hydrogen smashed into each other with enough force to create helium, releasing vast amounts of energy and light. These spheres, that fused hydrogen into helium, were the first stars.
Now, smaller stars only fuse hydrogen into helium. The gravitational pull of the mass of the star isn’t enough to counteract the outward pressure of the fusion, so the density can never be great enough for further fusion. Bigger stars, however, are denser, and denser stars can fuse that helium into heavier elements — like carbon and oxygen. Even more massive stars can fuse those elements into even heavier elements. Like iron.
When these supper massive stars die, by blowing up, they create new clouds of gas and heavy elements from which new stars and systems are born. These second-generation systems (like ours) now have the necessary products for life to exist.
Is this process tuned so perfectly that any variation would see the universe devoid of life? I don’t think so. There is room to move, and it’s only human subjectivity that tells us what is “a lot” of movement and what is “a little”. Plus, we don’t know the nature of the existence of the universe in something greater, how many other universes there are, or how the inherent laws of this one are linked to each other. Nobody knows if the movement of one “law” wouldn’t see a compensating movement in another.
From here, for now, it’s all conjecture. Claiming to know an answer, any answer, especially the make-believe “God did it” answer, is folly.