Edit : solved. The missing step was the definition of the source in the Collection list wrapper.
Following the instructions on Introducing dynamic CMS and Ecommerce galleries | Webflow web design - YouTube, I created a devoted ‘Multi-Image field’ to create a gallery.
However, while inspecting the product setting, I see that a native multi-image field ‘More images’ already exists in the ‘Media’ section.
But the images of the gallery (ie collection list) cannot be imported from this field, only in the additional field created for this purpose.
It would be great to be able to use this ‘more images’ field (and thus avoiding redundancies and saving a custom field).
Anyone having already faced and solved this issue ?