Fiddle-faddle is an old-fashioned word; its origin is late 16th century, and it is a reduplication of fiddle.
It means trivial matters or nonsense. In this sense, it can be used as a noun or an exclamation/interjection.
It can also be used as a verb meaning to bother over trifles*, fuss or waste time. You can be a fiddle-faddler.
I understand that Fiddle Faddle is an American popcorn product, which is interesting. It is also the name of a musical composition by Leroy Anderson – I’ve listened to it; it’s quite nice. If you use Spotify, here it is:
*Not the desserts, but something of little value or importance.