I remember using this window object many years ago. Sadly it doesn't have a proper symbolic floorplan representation, if I recall correctly. You can try setting the floor plan display of the window to projected instead of symbolic.
To make this shape yourself, you can create your own window by drawing it with walls and slabs. There should be some tutorials for this floating around, probably in the helpcenter too.
Finally there are some third party addons that will let you make these shapes (probably).
The only fully parametric "freeform" window with all the standard documentation features and every other possible window function you could think to apply to your freeform window. Legitimate GDL content created by an Archicad user of 20 years (13 of which have been fulltime GDL) working with firms all around the world. This tool is about to turn 10 years old and is capable of replicating any opening assembly and has a unique and powerful catalogue feature where you can save your freeform shapes to a database that the tool can access from any project. Plus you can access manufacturer's databases of their freeform (or normal) window assemblies: https://cadswift.com.au/products/Infinite-Openings.html
Unfortunately it is not free, and is another subscription, but we simply cant create such tools with generating a revenue to support them. The tools do not generate enough to cover their development cost so we still do a lot of unpaid development time, as does every 3rd part developer who enjoys coding, part of our leisure is our work, so we don't really work as long as it looks. However, your support would make a difference, so I hope you will consider Infinite Openings and the rest of our Archicad libraries.
Creator of Cadswift's parametric GDL libraries
Creator of Infinite Openings and Component Catalogues
Push the envelope & watch it bend