QUANTUM VS CLASSICAL. “From the point of view of Newtonian classical mechanics, these two characteristics imply that a photon should not exist at all.”
https://opentextbc.ca/universityphysicsv3openstax/chapter/the-compton-effect/#:~:text=The%20Compton%20effect%20is%20the,wavelength%20of%20the%20incident%20radiation