Is there a legitimate Sharia issue in selling sweets that include sugar and white flour in their manufacturing, due to the potential health harms that may result from them?

There is no harm in manufacturing and selling sweets, because the harm referred to is not of a degree that would cause prohibition. The harm varies according to the quantity and the person's health condition, and the one who consumes the sweets is responsible for observing that, not the one who manufactures and sells them.