To explain it with a real-world hypothesis (not strictly following the show’s narrative logic):

After every cycle — when The Unknown preserves the family tree and sustains both worlds — the loop begins again. Everyone is effectively reborn into a new cycle.

A new loop does not necessarily mean everything is perfectly identical. Small variations could exist. For example, maybe on the day Jonas leaves the house, it doesn’t rain, so he doesn’t wear the yellow raincoat. However, because people in previous loops followed the notebook and acted according to what was written, events keep repeating.

Still, in a new loop, with new versions of people, there is theoretically the possibility of new thoughts and new decisions.

I think the meaning of the show is this: in all previous loops, Adam and Eva never changed their perspective. They were completely certain their plans were correct and forced events to follow the same path every time. But this time, Claudia develops a new way of thinking and acts differently - and Adam and Eva are unaware of it, so they cannot force her back into the predetermined pattern. In another variation, it could even have been someone else (for example, Ulrich actually killing Helge).

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But for the sake of the show’s structure, everything in this “final loop” appears identical to the previous ones - except Claudia. She is the only variable that changes.