In a nutshell: Cooking is perfectly fine.
First, the main concern about nutrition is vitamin C. However, cooking fruit doesn't significantly affect nutrient absorption because fruits naturally contain relatively low levels of nutrients, especially vitamin C.Take apples as an example: even when eaten raw, consuming one apple daily provides less than 10% of the body's daily vitamin C requirement. Other nutrients in apples—such as potassium, magnesium, pectin, and fiber—are heat-resistant. Beneficial polyphenols also suffer only partial loss during cooking.
Therefore, in this sense, fruits can absolutely be cooked before consumption, as they are not primary sources of vitamin C even when eaten raw. This applies equally to easily cooked fruits like pears and peaches, which also have relatively low vitamin C content. Cooking them poses no issue.
However, one consideration is that cooked apples are more easily absorbed, and their sugars can cause blood sugar fluctuations.Unlike when eaten raw, where the intact cell walls of apples delay sugar absorption to some extent, minimizing the impact on blood sugar compared to cooked apples. This principle is similar to why diabetics should minimize porridge consumption. The difference between raw and cooked apples is akin to that between rice and porridge—both cooked apples and porridge cause blood sugar to rise more rapidly.