The arrangement varies. A shared-looking switch may control selected lamps, while another cavity's light may follow its own door or function setting.
What the observation means
A dark cavity therefore does not prove it has lost all power. Conversely, illumination does not establish that its heater is working. Keep these observations separate when describing a multi-cavity cooker.
A useful next step
Check the lighting section of the manual and note which cavity is affected. If a bulb replacement is owner-permitted, use the specified compatible type and procedure. Do not explore wiring between cavities because one lamp behaves differently from the other.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.