The only limitation is the project size, apparently as soon as the project gets bigger than 32bit addressable space (4GB) you will not be able to open it on 32bit system.
You can open the Task Manager (CTRL+ALT+DEL) and there you will see how much memory ArchiCAD is using. I don't think you need to start worrying if it is well below 2 GB (2,000,000 KB).
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
It displays the available free RAM you have that no application is currently using, the higher the number the better cause it means your computer has more resources available.
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