Hello Magda,
It would be helpful, if you also specify the current processing stage and provide the screenshot of the expended details section of the progress dialog to understand, whether the current stage is assumed to use GPU or not.
As for the graphs in the Windows 10 Task Monitor on the left side of the window, are you able to provide any reference links where it is clearly described, what mean the percentage for those graphs? I recommend to open the full page related to each GPU and switch one of the graphs for your NVIDIA card to "Cuda" option and check the utilization of the GPU, providing that the current stage is GPU-supported.