Problems with importing 3D model

General Questions
1

Hello,
I am trying to use the PREPOMAX program to calculate a 3D thermal bridge. However, I have a problem with importing the 3D geometry. When I use the IGES format, the solid modeled object breaks up into shells. When I use the STP format, the program imports only one of the objects.
I also tried different formats via FreeCAD.
Can you please advise me where I might be making a mistake?

thanks

2

Exporting from FreeCAD can be tricky. Do you select all the objects in the tree before exporting to STEP (this format is the preferred one) ?