The magnetic force can't change the speed, so it can't change the KE.
Work Step by Step
The magnetic force that acts on a charged particle is always perpendicular to the particle's motion. There is no component of the force that acts along the instantaneous direction of motion, so the magnetic field cannot speed up, or slow down, a moving charged particle. Therefore it cannot change its kinetic energy. Speed or KE doesn’t increase because the force is perpendicular to the velocity, doing no work on the particle.