Prior to export, use Apply Structural Attributes to Slab/Free/Linear Form to apply Structural data to the slab or wall. This converts all existing features to ISM openings and/or modifiers. They can then be exported.

With the slab containing the Structural data attributes illustrated above, the changes to the form features can be viewed in the Building Element Info dialog’s Features tab.

After export (using the Create ISM Repository or Update ISM Repository tools), cuts, openings and protrusions appear as ISM entities Surface Member Opening and Surface Member Modifier.