Not sure if this will help but I believe you need will need to change the floor plan cut height as it would typically be at 1100mm or 3.6 feet. It may be that the window is below this height and is not being cut through.
If you go to the view settings of the plan on the project map and the under 2D/3D Documents tab click "Floor Plan Cut Plane Settings" it will allow you to reduce the cut plane to a level that will go through the window and it should then show up in plan.
ArchiCAD 24 NZE FULL
Windows 10 Pro 1909
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