In the “files” part some folders do not have thumbnails although their contents are recognized and have thumbnails. How to fix this?
You can add your own artwork for folders which will be displayed when browsing directly via folders.
Alternatively, you can use the library and this will provide a more consistent experience with artwork at all levels, automatically.
Some more info on the options for manual artwork and metadata can be found here.
D’accord merci beaucoup pour cette réponse !