This was in ArchiCAD 11.
But I think it was not part of the default ArchiCAD Library. It was part of the ArchiCAD Interactive Training Guide (the one with the Massaro House). The reason I remember is because I created that guide and I had to create this special Stair by modifying is GDL Script so we could place such a distorted Stair with a single click.
What I would suggest is that you create it using the Morph Tool then save it as a Stair Object.
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