The Snap To Scale option is missing or seems to do nothing in Mixcraft 10.

It won't seem like the Snap To Scale option is doing anything if you have the piano roll set to Chromatic or a drum map. Change the setting to a melodic scale like Blues or Dorian to see it work.

If you're using Step Mode, the Snap To Scale option will be missing completely. Change to Piano or Score mode to access it.