JitteryCoyote63 the agent.cuda_version (or CUDA_VERSION env) tell the agent which pytorch wheel to download. CUDNN library can be included inside any wheel and it will work as long as the cuda / cudart exist on the system, for example pytorch wheels include the cudnn they use . agent.cudnn_version should actually be deprecated, and is not actually used.

For future reference, dependency order:
Nvidia Drivers CUDA library and CUDA-runtime libraries (libcuda.so / libcudart.so) CUDNN library
(1) & (2) are usually system installed (or docker installed), (3) can have multiple versions in different locations (i.e. inside python packages)
If you are using dockers you can control (2) as it will be part of the docker.