Search BIMComponents (you can do this from your window settings dialogue) for "Window".
You will find one called 'FreeForWindow' (not sure if this can do curved top) and another called 'Polyfenster 1' that looks like it can.
I haven't used these so can't say what they are like but they are free.
Another alternative is to make the window from slabs in plan and save it as a window object.
It is not adjustable then but you et exactly what you want.
http://helpcenter.graphisoft.com/tips/archicad/library/how-to-create-custom-window/
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11