Is it possible to loop over contents of folder?

Is it possible (with twig) to loop over the content (for example images) of a folder?

Yes, through a plugin using PHP's scandir if you explicitly need to target a Folder, but if you are after Media within a Page then you should be using Grav's Media-mechanism: https://learn.getgrav.org/cookbook/general-recipes#creating-a-simple-gallery