It looks like you have flip normals, you can select everything in edit mode and do shift+N, it should fix it.
It’s because the object doesn’t have the support edges necessary to properly work with subdivision.
Subdivision turns faces into curves that go from an edge to the next. If you want a corner to stay sharp, there needs to be edges close to that corner to limit the curve’s ends.
A way you could do this is by beveling every corner edge, every edge you want to stay where it is.
If you want to transform a cube in a sphere (or a blocky shape in a much smoother one) you are.. RUINING THE OBJECT - basic - SHAPE.
This is how the subdivision surface - basically - works: gives you some smoothness at the price of precision.
First:
What exactly do you mean by “ruin the shape”.. what is this supposed to look like ? What clue do “we” have to judge or give any “advice” ??
Also:
If you are willing to share your file.. then one might have a look into this.. like for example:
oki-complexObjectShape.blend (130.7 KB)
This “visual exaggerated bevel” might be even wanted.