Hi Diana,
If you only want 1 wall then the only way I know of doing this is a work around of copying the wall from the story it is on and pasting it up to the next story. Then select this wall and explode it. It will then be just 2D elements. If you have Autogrouping on it will be grouped.
I usually do this kind of thing with 2 walls stacked up so that a wall shows on both storys but this can be complicated if there are tall openings that you want to show on both storys.
Hope this helps.
Gerald Hoffman
“The simplification of anything is always sensational” GKC
Archicad 4.55 - 27-6000 USA
2019 MacBook Pro-macOS 15.0 (64GB w/ AMD Radeon Pro 5600M GPU)