> That said, I don't know how nixpkgs can use Conan in an offline fashion (and am not familiar with it at all yet).    Looks like you just can't. :|    There's an open issue for it and it suggests manually coping the cache after running it on another machine which is online, which doesn't fit well.    https://github.com/conan-io/conan/issues/5575#issuecomment-518144576