The neutral line also comes from the power plant, and the neutral line is the neutral line. The generator only has three phases, but when passing through the step-down transformer (DY connection), the secondary side of the transformer brings out a cable from the neutral point. This is called the neutral line, which is also the zero line. mentioned by the poster.
The fact that the poster can think about the final destination of the neutral line shows that the poster is also a person who likes to think. Our electrical network is a mesh structure, and the neutral line comes out of it. this transformer will eventually be connected to another transformer.
I also suggest that the poster take a look at the TN system. The neutral line must be grounded.