Must I make up for the Ramadan fasts I missed in the year 2000, after the kidney removal surgery due to which your doctor forbade you from fasting?

Allah has permitted the sick to break their fast in Ramadan, with the obligation to make up the missed days, as He says: ﴿But whoever among you is ill or on a journey, then [he is to fast] a number of other days.﴾

However, if the illness is chronic and incurable, then only expiation is due, which is feeding one poor person for each day, based on the statement of Ibn Abbas regarding the interpretation of ﴿And upon those who are able [to fast, but with hardship] - a ransom [as substitute] is feeding a poor person.﴾: "It refers to the elderly man and woman who are unable to fast, so they feed a poor person for each day." The amount of food for feeding is estimated at one mudd of food (approximately 750 grams).

Therefore, if fasting affects your health, as confirmed by a trustworthy doctor, then do not fast until you are able to fast, either by making up the missed days or by performing it on time. And if the illness persists until the next Ramadan begins, then there is no expiation due from you for delaying the make-up fast, because you are excused.