Root Motion application has changed in 2018.3 to make it more coherent.
To reproduce the behaviour of Root curves (Root T and Root Q) with ApplyRootMotion OFF in 2018.3 and following, please turn on Apply Root Motion, and implement OnAnimatorMove like this:

public class RootMotion : MonoBehaviour {
public bool enableRootMotion;
private Animator animator;

private void OnAnimatorMove()
{
if (animator == null)
animator = GetComponent<Animator>();

if (enableRootMotion)
{
animator.ApplyBuiltinRootMotion();
}
}
}