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.