I have notebook with RTX2060 on windows 10. Running the interpolation, I get 100% on the CPU but only 4-8% on the RTX2060. Is this the intended operation? I would have thought the GPU would be utilised more. This is using windows task manager to view the usage.

It really depend on the settings you are using, if you are using PNG export and saving it in a HD instead of a SSD, it will bottle at the CPU. But what you need to check is the CUDA usage. Usually GPU usage is low, but CUDA is close to 100%