GTA V with minimal GPU demand and maximum CPU activity
Task manager appears to misreport GPU usage, so disregard it.
Or it might be checking the iGPU directly. Or you're really playing on the iGPU.
This seems odd since Task Manager indicates it's the NVIDIA. This might be due to the Innotec tuneUp OC tool displaying a GPU loading of around 60%.
Download and execute GPU-z, navigate to the Sensors section, and verify if the output matches.