Dr. Bowser did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Dr. Bowser's attire consists of a white lab coat, a gray undershirt with a hexagon pattern reminiscent of his shell, and a stethoscope around his neck that features his signature icon on it. He also wears a head mirror, and the chains around his arms and neck are white and gold rather than black and white. Interestingly, Dr. Bowser's outfit is reminiscent of his wedding outfit in Super Mario Odyssey.