Where people get into trouble is their overall calorie intake and the breakdown of their macros, it's not uncommon for people to get too many calories from fats or carbs. If you're sedentary you don't really need a lot of calories period. But if you're keeping an eye on all those things a bowl of oatmeal in the morning isn't going to kill you.
Edit: Here's a list of cereals and their nutritional info: https://www.bhf.org.uk/informationsupport/heart-matters-maga... Note that at the recommended serving size, obviously some are more healthy than others, but frankly none of them are really going to kill you. A serving of cereal is only about 100-250 calories. The problem arises when you eat multiple servings in one sitting.