You can safely store food in the refrigerator without covering the food.
But if you put food in the refrigerator and leave the food uncovered then the food can absorb smells and odors of other food.
So your food in the refrigerator left uncovered can take on different tastes of the other foods.
So whenever I put foods in the refrigerator I always put the food in sealed airtight containers to keep the odors out of the food.
Some other foods can taste bad when other food odors mix in with the food when they are not sealed in the container.
So you do not have to seal food in containers or wrap them up when refrigerating them but it is recommended to wrap the food up or seal the food in airtight containers to help keep the odors off the food.