A cover changes the food's exposure to steam and how pressure or moisture is managed. A recipe designed for an open perforated tray may not suit a sealed container.
What the observation means
Use only containers approved for the cooking method. Ordinary storage packaging is not automatically heat-safe, and sealed jars or unsuitable lids can create hazards. The oven's steam setting does not override the container manufacturer's limits.
A useful next step
Follow a suitable recipe and accessory guide. Record whether the container was covered if the result was unusually slow or wet. Do not improvise by sealing vents, tightening lids or increasing temperature to force steam into packaging that was never intended for oven use.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.