{SOLVED}problem about bake from high to low poly

Hi.
The optimal topology for a gaming asset must:
- have significantly lower polycount than the high poly version;
- be reasonable. For example, the fold at the back needs extra definition to look smooth, the collar does not because it is flat;
- support the functionality of the item. For example, breasts expand in circular motion, so there topology must be circular as well. Where an arm bends, there should be an edge loop and extra edges on the elbow.
Here's an example

The current topology does not fulfill any of these requirements, so there is not much difference between the original and the retopologized versions
Also, for the future, if the shape of the patterns are symmetrical, keep symmetry enabled, otherwise you're just doing twice as much work

As for the normal map, the extrusion is set to a very high number, the mesh itself is only about 2 mm in height, so you're getting this weird result
You should separate the shirt+skirt from the coat and bake them separately

Baking a normal map is done at the end, once your uv_0 is re-arranged. If you're doing it just for the sake of learning this subject, choose a different item. As I said at the beginning, it is holding you back and is making it difficult to learn the basics.