to all the above fruitfull explanations I might just add some comments.
I you do such an exchange try to use only one classification system, especially when you migrated the project from 20 to 21. As Laszlo mentioned, the two programms have different classification "systems".
In Solibri you won't be able to see the apropriate IFC Entity such as IfcSlab or IfcWall. Solibri also has an internal interpretation of these enteties, hence called Slab or Wall...or an IfcBuildingElementProxy is Object. But if you really want to look at the entetie, try usind BIMcollab ZOOM from Kubus. It is an IFC Viewer with displays the Entity and the PredefinedType.
And don't forget that by exporting in IFC2x3, you have just a Reference View Model
The BIMster @ AllesWirdGut
Currently: Archicad 26
User since Archicad 6.5 (2001)