You won't do this with any of the standard windows.
Try searching for 'freeformwindow' (all one word) in BIM Components.
This will give you a window that you can create in (almost?) any shape.
Or search here and in HELP on how to create your own custom windows.
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