Samsung RF268ACRS/XAA

I have a Samsung French door model RF268ACRS/XAA. Fridge works great (coldest beer in town!) but freezer will not get cold. I assume not a refrigerant issue?? Inverter board on back shows solid red light so should also be fine?? Fans in freezer spin freely. We replaced the temperature sensor AND the defrost thermostat in the freezer compartment which didn’t fix. What should we try next?