What is the ruling on fasting for a kidney failure patient after a kidney transplant, and what is incumbent upon him if he breaks his fast based on the advice of some doctors, knowing that he has paid expiation for this breaking of fast?

The days you missed fasting and paid the fidyah for do not need to be made up again, because you fulfilled what you were commanded. As for your fasting thereafter, the matter is referred to trustworthy doctors. If they differ, then it is obligatory to follow the most knowledgeable, pious, and religious among them. If the doctor determines that fasting will harm you, then it is permissible for you to break your fast while feeding the poor. But if he states that you are able to fast, then it is obligatory upon you.