How do I rotate an object to the cursor?Where is the mistake in the code?

Game in 3d. it is necessary to rotate on 1 axis. I’m from Russia.

	void Update () {
		var mous_pos = Input.mousePosition;
		mous_pos.y = 0;
		var tr = transform.position;
		tr.y = 0;
		var nap = Camera.main.ScreenToWorldPoint (mous_pos - tr);
		transform.rotation = Quaternion.LookRotation (nap);

Your cursor is on 2d screen while an object you are trying to rotate is in 3D scene.
You need to perform a raycast from screen to the 3d world in order to get a point in 3d space.
Here is a snipped code for you:

    public LayerMask layers; // layers filter for where you want your cursor to raycast
    public Camera camera;
    public Transform myObj;

    void Update()
        RaycastHit hit;
        //Create a ray from screen cursor to the world
        Ray ray = camera.ScreenPointToRay(Input.mousePosition);
        // perform raycast and get intersection point
        if(Physics.Raycast(ray, out hit, float.PositiveInfinity, layers)) {
            Vector3 lookPos = hit.point;

            // if you don't want your object to rotate up and down
            lookPos.y = myObj.position.y;