A pull-out shelf or support accessory has the purpose and load limit specified by its manufacturer. It is not automatically designed to carry a person.
Understanding this situation
Using it as a seat or step can damage the kit and destabilise the arrangement. The appliances' normal weight does not mean every projecting part can support additional concentrated loads.
A useful next step
Use the accessory only as instructed and keep children from climbing on it. If it bends, cracks or no longer closes normally, stop using the affected arrangement and seek assessment. Do not add improvised brackets to restore confidence.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.