Full modulation of an FM broadcast station is only 75kHz. Since the carrier is at such a high frequency of around 100mHz then you won't see the tiny amount of frequency deviation on an oscilloscope.
There is a 'scope technique where you use both hoz. & vert. inputs. You end up with a Bezel function or Lazarus function...
I sometimes used it at work 30 years ago and can't remember the details.