A lot of clues are provided, but after each follow you will find a fork in the road ahead, which is really a headache

I read it twice. 4 or 5 years later. I watched it for the second time yesterday. There are still many questions. I have written a few of my questions here. I hope everyone can talk about their own interpretations based on their own understanding.
1. How did Downey use his superpowers to send the relic back? In the final episode, Downey drove Gretchen to the distant mountains, watching the storm in the town from a distance, (wormhole?) He burst into tears, knowing the fact that he was going to die soon. Then what method did he use to send the plane engine that fell from the sky back 28 days ago? The engine of this plane should be the plane that my mother and sister took, right? Was it an accident that was directly affected by this storm? Why did he deliberately drive to the mountains? Dodge the police? Dodge the storm? Or do superpowers require solitude? If he gets caught by the police and goes to jail, he can't return the relic? Or did he not do anything special to send the relic back, and Downey had no choice but to passively watch everything happen?
2. What is Downey going to do for the world? Is Downey the savior? Or is it just a prop?
3. Does this 28-day offline world exist only once or countless times? If Downey in question 2 is just a prop, and the offline world will exist countless times, is it a bit like Haruhi Suzumiya's never-ending August? August was spent countless times, and Suzumiya did not allow time to move forward until Ah Xu finished his summer homework? Downey kept looping through 28, until he realized that he knew everything he wanted to die, and the cycle ended. However, some small plots in the film may suggest that it is repeated multiple times in 28 days. His right eye was blinded by a gun. Downey mentioned to Gretchen that he once set fire to a house.
4. Was Shi Tai once a living body recipient? One explanation is that the old lady was a former recipient of a living body, she chose not to die, and then she had to die alone?
This movie gives me a lot of headaches, I think there can be many explanations, but each explanation seems to explain only part of the problem, so far I haven't thought of or found a single clear explanation that can explain all the problems. Maybe the director has a lot of mysteries, but the truth is indistinguishable, making this film an open text that can be interpreted in multiple ways. really headache

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