the idea is to copy the shadows from your 3d view and paste them into the floor plan where you can change the shadows fill to a to a gradient fill.
You will need to view the plan in 3D using the Internal Engine. Adjust the Sun Azimuth and Sun Altitude and the surround the area with the Marquee tool and Copy. A menu will pop up so you can copy the shadows only if you like. Paste the shadows into the floor plan. they come in as a fill that you can edit.
ArchiCAD 25 7000 USA - Windows 10 Pro 64x - Dell 7720 64 GB 2400MHz ECC - Xeon E3 1535M v6 4.20GHz - (2) 1TB M.2 PCIe Class 50 SSD's - 17.3" UHD IPS (3840x2160) - Nvidia Quadro P5000 16GB GDDR5 - Maxwell Studio/Render 5.2.1.49- Multilight 2 - Adobe Acrobat Pro - ArchiCAD 6 -25
