Is there any reason why i shouldn't upgrade my OS from Win XP32 to windows 10?
Are there any compatibility issues?
Archicad 12 was released 13 years ago.
You should not expect it to be fully compatible with Windows 10.
You can try but I don't know if it is possible to do real production work with it. You need to test it on a Win10 system, and if it works, you can upgrade your own system.
You will save more time upgrading your Archicad then dealing with legacy software for a legacy system.
Since the system requirements for AC10 are so minimal (in comparison to the machines available today), you can try running it inside a virtual machine with XP.