Is ablution (wudu') required when air exits the anus without an odor, and it is not thought to be wind like the known wind, due to a previous operation for an anal and coccygeal fistula?

Everything that exits the anus nullifies ablution, whether it is gas or something else, and whether it has an odor or not. However, if it is merely a whisper (waswas), then do not pay attention to it. But if you are certain with absolute conviction that something has exited, then you must perform ablution. If the discharge is continuous such that you cannot find time to pray with a valid purification, then your ruling is that of one afflicted with سلس (incontinence), so you perform ablution for each prayer after its time has begun and pray as much as you wish.