Yes, you can still refrigerate an apple that has been left out overnight, but there are some factors to consider before doing so.
If the apple has been left at room temperature for an extended period, it may have been exposed to bacteria and might not be safe to eat. Bacteria can multiply rapidly on the surface of fruits like apples, especially if they are cut or damaged.
Before refrigerating the apple, check for any signs of spoilage or changes in appearance, such as mold, mushiness, or off smells. If the apple looks and smells fine, it should be safe to refrigerate.
Keep in mind that refrigerating the apple at this point might not reverse any spoilage that has already occurred. It may slow down further deterioration, but the texture and quality of the apple may have been compromised.
For best results, it's generally recommended to store apples in the refrigerator right after purchase or when you bring them home. Refrigeration helps to preserve their freshness and extend their shelf life. If you have doubts about the safety or quality of the apple, it's better to err on the side of caution and discard it to avoid any potential foodborne illnesses.