If the Block Universe is true, and if the Rebound Universe is also true where the universe goes from Big Crunch to Big bang then doesn't that mean that the Block Universe is shaped like a circle where history repeats the exact same way and so do we - therefore wouldn't that verify Nietzsche's Eternal Return theory to be true?
Nietzsche's eternal return is a thought experiment for his existentialist ethics, not a metaphysical hypothesis. Roughly, the idea is that, as I reflect on the decisions that I've made in life, I imagine that my life will endlessly repeat in exactly the same way. If this thought makes me happy or excited, because I get to endlessly relieve my great triumphs and accomplishments, then I've lived well.
Nietzsche doesn't care whether or not the eternal return is actually true. It's a heuristic to evaluate the quality of our lives.
Now, in terms of physics, general relativity does allow the existence of "closed timelike curves." The basic idea is similar to science fiction stories (movies, TV shows) that feature "time loops" as a plot device. However, in those stories, the protagonist has some way to carry information from one loop to the next, usually deja vu or a vague memory. That wouldn't be the case with actual closed timelike curves. Closed timelike curves aren't like a dog chasing her tail, spinning around and around. They're more like a statue of a snake with her tail in her mouth. There aren't actually iterations or loops of the closed timelike curve; it's just that spacetime is structured in a closed circle.
Closed timelike curves are possible in general relativity, but AFAIK they require very specific arrangements of matter, and have never been observed in the real world. (IIRC the original example to show they were possible had a universe full of motes of dust spinning in a particular pattern.) So there's no reason to think that we are living in a closed timelike curve.