Which version of CUDA are you building against? cuDNN 8.0 is supported by CUDA 10.2 and 11.0 only although I would assume if its pre-installed then the correct version of CUDA would also be present? I would see this for cmake switches which may help you to find cudnn.
In my experience on ubuntu if its installed cmake will find it, what are your cmake commands and output and are you using the same commands as you did on 4.5.1?