Nutella is a chocolate hazelnut spread that contains sugar, vegetable oils, and other ingredients. It does not need to be refrigerated if left out overnight or for a short period. Nutella is formulated to be shelf-stable at room temperature.
The key to keeping Nutella safe to eat is to store it properly and follow the manufacturer's recommendations. After opening the jar, make sure to keep the lid tightly sealed when not in use to prevent it from drying out or absorbing any odors from the surroundings.
However, if you live in a very hot and humid climate or the temperature in your kitchen is consistently above 75°F (24°C), you might want to consider refrigerating Nutella to prolong its quality and prevent any potential oil separation. Cold temperatures may cause the spread to become slightly firmer, but it will become smooth again once it returns to room temperature.
In summary, it's generally safe to leave Nutella out overnight or for a short time, but for best quality and to avoid any potential issues, it's advisable to store it in a cool, dry place and keep the jar tightly sealed when not in use.