Help! The mesh is imported into the program incorrectly

Hello!
I just looked at your mesh and the issue is the normals are facing the wrong way. If you select in blender to show the faces orientation you will see this:
You can fix it selecting all the red and with Alt+N then select invert.
After that you will see everything ok in S4S.

I haven't done any CC for CAS but I think your poly count is too high I'd try to lower it using merge by distance