Try to select part of the model with the thick marquee and see if that is generated in 3D easier.
Try to avoid high polygon count objects (like trees, cars etc.)
Try switching of the 3D in sanitary objects, like toilets, bathtubs etc.
Try switching off Layers you do not necessarily need to see in 3D (e.g. interior furniture when you are checking the exterior look of the building.
In short, try to find the size of model your computer can handle and stick to that.
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