Hello Inumaki. Can you post an image or a video of that shading problem? Just so we can see and troubleshoot from there.
If I had to guess, it’s probably a problem with the topology. Maybe you have double vertices? Select all and “M” to merge by distance. Maybe your faces are too stretch? See if you can use “J” between two selected vertices to cut through them if you have a very elongated face. Maybe you have some flipped normals? Select everything and Shift + N to recalculate your normals.
