This works for me:
1. Place a Fill on the Floor Plan, assign Empty Fill to it.
2. Slect it, copy to Clipboard.
3. Go to Fill Types, rename Empty Fill to Empty Fill-2 or something. OK Dialog.
4. Paste Fill. The referenced Fill type (Empty Fill) will be created among the Fills and now you have two Empty Fills.
If you had not renamed your fill type before, no new fill type would have been created because the program would have found the Fill type it referenced by name.
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-Ac28