Cats like to dig around in the cat litter before they use the litter box. Once they’ve found the perfect place to poop, they dig a hole, do their business, then bury it.
It’s all part of normal cat behavior, territory marking, and cleanliness. However, it’s normal for cats to scratch the walls near the litter box and the sides of the litter box. This just means they’re making sure they’re using all the available cat litter.