it refers to being visually appealing, the quality of this. Abstract noun refers to a thing that has no physical form. This means we cannot see or touch it. However, we can see something that is picturesque, similarly to how we can see something that is beautiful, however, beauty is the abstract noun.
If a noun is abstract, than it will describe something you cannot see, hear, taste, touch or smell. Since picturesque means visually attractive, especially in a pretty style, it is not an abstract noun. Hope this helps!
