First thing to check, any air coming into the refer area from the fan? If not then you have a restriction. Second, if this is the case, best thing is to manually defrost the unit. If you can move stuff to a temporary unit (another fridge/freezer, cooler, etc) defrost by unplugging the unit, wait several hours, could be several hours unless you speed it up with warm air introduced to the freezer section. Then once defrosted, restart the unit and monitor to see if it is cooling. Check the temp in the fridge and freezer. If it seems to be working fine and cooling the fridge side, then you have a defrost cycle issue and not a coolant(Freon) issue. This could be a number of parts, a thermistor, defrost heater, timer, circuit board, etc. The first place is to monitor the defrost cycle. If you can manually advance it and it seems to defrost, then you have a possibly timer issue. To monitor the defrost cycle, you need to have a clear view of the coil inside the freezer. If it melts the ice off the the coil, then your defrost cycle is fine. If not, you need to test the thermistor for the heater. If it is good, then the heater. If those are good, then the cycle timer could be bad. Im not sure how to check or manually change the cycle on a newer digital fridge, but older ones you can manually turn the timer to different parts of the cycle. You can turn it and listen carefully to see if it is making noise, also turn it until it clicks then listen for the fridge to do something. If the fridge is cycling on and off or sounds normal, then your issue is not the timer and would lead back to the defrost cycle. Most non-cooling issues I have ever come across (DIY guy that helps friends and family) are the thermistor or the timer.
