you should follow these instructions: https://hashcat.net/faq/wrongdriver
and install the driver from your vendor page (https://www.nvidia.com)
only if you are very comfortable with your operating system packaging system and know what the packages do and what list of packages you need to get OpenCL working, you could play around with the packages...
My guess is that the nvidia package is the raw driver without opencl/icd etc... you would probably need to install several packages from apt to have the full features that the drivers from https://www.nvidia.com provide (because most ubuntu/debian users won't do anything OpenCL related and therefore do not need more than the display showing some pixels)
and install the driver from your vendor page (https://www.nvidia.com)
only if you are very comfortable with your operating system packaging system and know what the packages do and what list of packages you need to get OpenCL working, you could play around with the packages...
My guess is that the nvidia package is the raw driver without opencl/icd etc... you would probably need to install several packages from apt to have the full features that the drivers from https://www.nvidia.com provide (because most ubuntu/debian users won't do anything OpenCL related and therefore do not need more than the display showing some pixels)