|What key is this song in?:
Theoretical Db or Bb minor. Or Gb lydian? But this answers are kind of weird to me since the Db chord is hardly used, Bb does not sound as the tonic and the C flat doesn't sound here as the strange 4th step of the lydian mode.
If you need a key, I prefer Bb minor because of the F chord in the piece.
I rather should say that most pop songs aren't using 'keys' anymore (meaning scales, with the first step as the tonic)
but rather a sequence of chords, in this case Gb, Bb minor, Ab, and the very beautiful combination Eb minor - F!