I'm new to this 3D animating so I need a bit of help when there's troubleshooting in the air! I have an issue when I apply experimental subsurface modifier, where the mesh seems to be doubled or scaled inside out if that makes sense. I did some troubleshooting myself, and my own thoughts were that it could be flipped normals. Although there were 1 or 2 flipped normals, fixing this didn't solve the actual problem. Then I looked for ngons, which I know is the case for some of the mesh, but for the rest of it I'm not sure what causes the weird effect.
picture #1: Picture of the entire model in rendered view, the black areas are not intended either, some of this could be ngons as I haven't fixed them yet
picture #2: this is a cube inside the full model, it's literally just a cube where I moved the vertices and used the mirror modifier on the y-axis