I have downloaded a glass PBR from CGAXIS (blender format), opened it in Blender and tried to apply it to a model I created. As you can see in the screenshot, it appears gray and opaque, not transparent as glass.
I have added sunlight; and I am in Eevee. The node set up looks correct. The material preview looks fine, but grey as well (see picture).
The texture I downloaded is this one: https://cgaxis.com/product/dirty-glass-pbr-texture/
I must be missing very basic something but what?