Carbohydrates are an important nutrient. You don’t necessarily need much, but “some level of sugar” is not an issue. Calories in and calories out are all the ultimately matter for weight loss, but different things affect how much you feel you need to eat, from the nutrients that make it up to how much volume it physically takes up, so losing weight it probably easier if you change what you eat. If you are eating calorie dense foods, its not going to have the volume to fill your stomach and it can be easy to overeat even if only consuming calories in one meal.

For me, only eating one meal a day is all it takes for me to lose weight without counting calories. But I do get fairly regular exercise as part of my normal activities and my unhealthy diet at includes foods that are not very calorie dense so I simply cannot eat enough calories in a single meal to overeat. I don’t go to the gym or dedicate time to exercise: I ebike to work most days (quite low intensity, but since its 1 hour each way, it still gives an extra ~750 calories) and beatsaber is a favorite game of mine. I don’t think going to a gym often is something that sustainable for most people. Different people find different things work for them. For some its just counting calories and strict meal planning, others its keto, etc.