Scenery is usually taken in the wide format, that why they call it "LANDscape." There are usually more materials on the sides than top (mostly blue sky), and if you include too much earth bellow, that distracts from the rest of the scenery. In photography, a rule of thumb is, you want to concentrate on 1 subject matter. In a scenery, your subject matter is the whole expanse, not any one single item.
Portrait, like portrait of a person, a pet, a plant, because these subjects are taller than wide. If you take these subjects in landscape mode, then the side stuff is going to distract from the subject at hand.
There are exceptions. I.E. you are outdoors, you are on a side of a mountain, you want to show how high the drop is. In this instant you take a picture of the mountain's ledge in portrait mode which will include the top of the mountain, and much of the drop as you are able, that gives the observer the sense of a big drop. If you take the same pix in landscape, it won't feel the same.
Example 2: You dog is chasing a ball, you want to show how hard your dog is working. So you shoot your dog in landscape to show him AND the ball at some distance.
Welcome to photography lesson 1.