It seems like I'm missing something basic, but I can't work out what it is:
I draw a basic 2D shape with lines, polylines, fills & hotspots. Select, save as object under Libraries and Objects & give it a name, save it to the embedded library. There is no preview picture. I can go to the object tool, find the saved object (preview window says 0x0) and place it, but nothing is visible. I can undo & redo placed object but cannot select it. It has been placed on the archicad layer and it's not a renovation filter issue. I'm using AC23, and I can place 2D objects I've saved with this method and imported from previous versions.
I was right - I was missing something very basic: Trying to create a 2D object from an elevation view, instead of from a floor plan window. The object was saved, but being 2D seen on edge was obviously not visible.