All of the ducks in the lightweight class are not flyers, the ones that fly are the bantam breeds and Muscovy (which is actually a different species than the other domestic ducks).
A lot of ducks can at least get a little airborne, maybe four to six feet in height and maybe fifteen feet distance. They usually don't do this as a habit to escape their pens, unless they are frantic under predator attack. It seems to be more a way to exercise occasionally or to get somewhere in a hurry.
That said, there have been occasional reports of Khaki Campbell and Cayuga that can fly some distance at roof-top height. I have yet to hear about a Welsh Harlequin that can fly, but I bet someday someone will have one. I hope they tell us about it!