Hello Riccardo Scagnoli,
Thank you so much for your questions. This theme is specially designed for magazine and we put a default image if featured image is missing. If you want to hide this, you have to add featured image on that post. Or, you can change the default image and put your own image as default image too. Also, you can hide the featured image on the single page too. Please follow the documentation to know more about the features.
Hope it will help you.
Regards,
Acme Supports