The temperature of the oil is too high, which scorches the sugar, so it is black. If you add sugar after cooking, it is best to add it when there is water in the pot, and it should not be too dry, or when it is almost out of the pot. Sugar is used to keep food fresh, so it won't burn.

Your recipe may be like that, but what we usually do is to fry the fat first, and then add soy sauce, salt and sugar. But recipes should be a more flavorful way. Try a few more times, hehe, I wish you good craftsmanship and a good appetite!