Some people say that losing weight comes down to 20% exercise and 80% exercise. There’s no exact percentage except eating more calories than you burn in the day. This magic is called calorie deficit my friend. The balance between how much you eat (not what you eat) and how much energy you use in the day (including exercise and just living).
Diet doesn’t have to mean being on a diet, eg. Keto, 5:2, Slimfast, WW etc. Diet simply means “the food and drink usually eaten or drunk by a person or group“.
Exercise significantly helps burning calories if you’re disciplined enough to avoid overeating. On the other hand, NEAT (Non-exercise Activity Thermogenesis) can contribute to a negative energy balance as well. For example, doing the house chores and going grocery shopping.