Paaasiii

Indeed, but B450 chipset doesn't allow the CPU to split its PCIe lanes. X470 has that capability, and you can find many of the X470 mobo supports dual GPU and capable of SLi or CrossFire. So X470 board are ideal for dual GPU setup.
 
Also, do note that PCIe from the chipset supports PCIe Gen2 only. It'll be way slower if running a GPU card.

well you only need to have 2 16x slots running at 8x CPU lanes each. 
 
that is the actual issue.