Thank you both!
It’s now working. For me, this is super n00b mistake   I had the Nvidia drivers and Cuda installed, but I’ve never done C++ development, so I didn’t have Nvidia’s cudnn installed.
I followed the installation instructions here for the “runtime library” and it linked the paths for me. I did see some notes about linking paths, but I didn’t have to once cudnn was installed.
https://docs.nvidia.com/deeplearning/sdk/cudnn-install/index.html#installlinux 343