Damage to adjacent cabinetry can indicate an installation, ventilation, sealing or use issue that cannot be assessed from the cooking result alone.
What the observation means
The location matters: a mark above a vent, beside the door and near an electrical switch suggest different questions. Do not cover the mark with trim or seal an opening before its cause is understood. Existing cabinet materials and clearances also matter.
A useful next step
Stop use if there is overheating, scorching or a burning smell. Record the affected location and when it first appeared. Leave removal of the built-in oven and inspection of concealed connections to a competent person rather than pulling it out yourself.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.