In Archicad, 3D views, 2D section views etc are generated using the 3D engine and show as "true" representations and results of your operations in the model.
The 2D floor plan view however is
symbolic, showing all the visible elements within its range. The elements show complete, not taking solid element operations into consideration.
If you want a "true" cut 2d plan view, you must make a 3D cut of the model and show it as an axonometric top view. If you like, you can save this view and overlay it with a floor plan view in a layout.
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