Select the Curtain Wall. Click the Edit in 3D text that appears in the middle of the Curtain Wall.
In the Toolbox, select the Accessories Tool.
You can either click a intersection point of Frames, then another one, then provide the orientation.
Or you can click a Frame, give the length of the Accessory and provide the orientation with successive click.
When you start creating it, check what the shadow line shows: it shows where the element will be created based on your input.
Loving Archicad since 1995 - Find Archicad Tips at x.com/laszlonagy
AMD Ryzen9 5900X CPU, 64 GB RAM 3600 MHz, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac27