bad new is as far as I know it will be a sensor problem. as with a lot of fridge freezers the sensor is attached to the evaporator before the foam is applied. to change the sensor involves digging a hole in the insulation while being careful not to damage the pipes. then installing a new one and re apply the insulation.
plus you have to find a suitable NTC sensor
all above is possible as other engineers have managed to find and fit suitable parts but its not easy. Beko don’t list a sensor on the parts list
never tried myself as refrigeration is not my area of expertise but maybe other members will jump in and confirm
Dave