I think most of the FCUs on the market (Daikin, Sinko, Carrier, Trane, York, etc.) are Multi-speed air flow (High-Mid-Low, and Super low in some models) and Variable water flow. Although 2-way motorized valve is mounted outside the FCU body, I believe most MEP engineers design variable flow system. However, ZoneHVAC:FourPipeFanCoil does not have such Capacity Control Method.

Is there any way to model FCU with MultiSpeedFanVariableFlow?

I always choose VariableFanVariableFlow as a makeshift. MultiSpeedFan is not suitable as its water flow is constant which results in huge defference in the chilled water pump energy consumption.