With relatively inexpensive USB-C docking solutions, there may be problems with the resolution, e.g. no 4K image in 60 Hz but only 4K 30 Hz, but as it was described, it could also be that the notebook cannot output any image via USB-C. There are models that can only receive and output data via USB-C. What notebook model is it? You can check with the manufacturer whether it can also output video signals via USB-C or not. Or the HDMI cable is simply not OK, that could also be the case, but I would check the model number of the notebook to see whether it can output an image via USB-C at all or not.