(5.5.0f3) Rigidbody2D still affected by Physics when IsKinematic is set.

It's actually a fix. Changing the body-type of a Rigidbody2D should do just that and only that and not also change its linear/angular velocity. Kinematic bodies can have their linear and angular velocity set and will move (unlike a 3D Rigidbody). A Kinematic body just doesn't reponds to physics forces (it effectively has zero mass similar to a Static body). A Static body ignores any linear or angular velocity set and forces applied.

If you want the body to stop moving then reset the linear/angular velocity. If you want the body to stop responding to forces then set it to Kinematic. If you want the body to stop and not respond to forces or ever be moved by yourself then set it to Static. Turning off simulation is super fast but that's for when you want the body, its colliders, joints, effectors (etc) to temporarily ignore all physics in the simulation (note that it doesn't change any velocities or properties of any of those objects).