A single slit diffraction pattern does not require interference. Diffraction, refraction, and reflection all can cause the path of light to not be in a straight line. Polarization involves interference. Laws are the same only on inertial frames with zero velocity. Laws are the same only in inertial frames moving at low velocities.
Laws are the same only on inertial frames moving at near light speed.
Laws are the same on all inertial frames. A super fast freight train has a 20 m long box car when measured at rest. You are standing on a railroad platform as a train is passing by. You observe and time a light beam leaving a flashlight and bouncing off a mirror in the front of the railroad car and returning. A passenger in the car also times the same event.