Hi and welcome,
Most probably Mono in 1 bus is not connected to In-2 Jack of your NI Komplete Audio 1. Please double check in the Studio > Audio Connections.
I would recommend to watch Steinberg Cubase Quick Start Video Tutorials.
Be aware, some menu entries has been renamed since Cubase 10:
- Devices = Studio
- Device Setup = Studio Setup
- VST Connections = Audio Connections