The windscreen wipers do not wipe clean? What can be the reason for this?

You selected both answer 1 (The windscreen wiper blades are worn) and answer 2 (There is an oil film on the windscreen), which are correct.

Windscreen wipers may not wipe the glass clean if the wiper blades are worn out, as old or damaged rubber cannot effectively clear away water and dirt. An oily film on the windscreen can also prevent the wipers from cleaning properly, causing streaks or smears. The windscreen heating, however, is not related to the cleaning function of the wipers; it is used mainly to defrost or de-mist the glass. In summary, always check the condition of your wiper blades and ensure the windscreen is free from contaminants for optimal visibility.