Telemetry data needs to come from the flight controller and run through an on screen display chip. The OSD is wired between the video signal from the camera and VTx. Many modern flight controllers have an OSD built it, or you can use a separate device like a MinimOSD. These can be annoying to set up, the best option is to get an OSD enabled FC like the Bardwell F4, CLRacing F4 or any of the newer Omnibus. These are simple to wire and are configured directly through the Betaflight (or iNav) configurator.