while this is true, the Save button under it is inactive and will not let me save the preferred name. Believe me, both my DH and I have unpronounceable names and would gladly go by our preferred names onboard. Staff doesn't even bother with our names, unless they are from the same countries and can actually pronounce them (which happens, but not a lot).
ETA: I had to refill all the emergency and other personal information in order to add a preferred name. Used the web version of the app.