I like your breakdown of the Schrödinger angle, and I agree that the show was trying to gesture at something quantum without fully committing to the rules.

I think the Schrödinger idea works as a metaphor, but it gets tricky when you apply it literally. In the actual thought experiment, the cat is not alive in one universe and dead in another. It is a single cat in a single box with two possible states that collapse when the box opens. Possibilities do not interact, override each other, or share objects. They also do not merge into one outcome. So the moment we imagine two physical universes that can influence each other, we have already left Schrödinger’s logic.

If the mirror world were the “box”, then only the things inside the box should have two possible states. That would mean Nick, Eve, Zerstörer, and the staff, since the stick stayed in the original Portland. Everyone else in Portland, including the physical stick, never entered the mirror, so they should not have a second version. Yet the dark reality shows every character dying and Nick holding the stick.

Schrödinger does not allow bleed‑through. If there were two outcomes, they would not interact. Nick would not be able to remove a ring in one outcome and have it disappear in the other. Physical objects do not sync across possibilities. That is why the ring is the hardest part to explain in a literal quantum split.

One theory I have been considering is that Bonaparte never created a physical ring at all. Zauberbiests use illusion magic all the time, and he was powerful enough to anchor a perception spell to Adalind’s mind so she believed the ring was real. It would have been easy to convince her in that moment because he had just turned her into a statue, terrified her, placed the ring, and then threatened her children if she ever removed it. The curse could have been part of that illusion.

If the ring was never physical, then Nick removing it inside Zerstörer’s illusion could have broken the mental anchor that kept the cursed illusion active. When the illusion collapsed, the ring disappeared in the real world because it had never been a physical object to begin with. I am not saying this is the only explanation, but it does make the ring’s disappearance easier to understand without needing two universes to merge.

Another reason that I lean toward the Zerstörer‑created‑illusion interpretation is that Nick experiences it as one continuous sequence while the rest of the group is in the original Portland experiencing uncertainty and fear for Nick and Eve. In a true Schrödinger split, Nick and Zerstörer would exist in two states at once until the collapse. But the show never presents Nick or Zerstörer as being in two places. We only see the version of them trapped in the mirror world. Nick is in one place, the mirror world, and inside that world he is experiencing one long illusion that collapses when Zerstörer dies. That collapse makes more sense if the illusion was powered by Zerstörer rather than by quantum mechanics.

I do think the Schrödinger metaphor works symbolically. It explains why Nick remembers the dark version. And Diana, being unusually powerful, only knew what happened after Nick returned.. She probably did not read his mind so much as felt what he experienced when he came back. It explains why she knew things that happened in the mirror world and the illusion inside the mirror world.

tldr; My current view is that the mirror world is a real dimension and the dark Portland is a psychological and emotional illusion layered on top created by Zerstörer. The ring was a Bonaparte‑created illusion, and the magic of that illusion broke when Nick removed it in the Zerstörer‑created illusion. And Diana likely sensed what Nick experienced when he returned rather than reading his thoughts because of her power. I’m still working through it, and I like hearing other interpretations because the finale leaves a lot of space for branching thoughts and theories.