You seem to install ollama as a service, this means systemctl status ollama.service should show you a running ollama service, listening on a port. It does not add ollama to your $PATH though.
For that you’d probably want to add pkgs.ollama to environment.systemPackages. Or, as you are seemingly trying to use it with cuda, use pkgs.ollama-cuda for both, environment.systemPackages as well as services.ollama.package = pkgs.ollama-cuda. (I think the latter should allow you to get rid of the custom LD_LIBRARY_PATH)