Quaternion.Lerp rotation is not smooth

Questions & Answers
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1

So, I am working on tower defense and now I am doing turrets rotations. I’ve been following tutorial on yt how to do rotation , and they’ve used

Quaternion.Lerp( startpos , enemy , Time.deltaTime*rotationspeed );

in it so I tried this as well.

Problem is , in video towers move smoothly between new targets but my towers just jump around really quickly and it bothers me. I don’t really know what am I doing wrong,

code for rotation:

[SerializeField] private Transform target;
[SerializeField] private float range;
[SerializeField] private Transform parttorotate;
[SerializeField] private float rotationspeed;

void Start()
{
    InvokeRepeating("updatetarget", 0f, 0.5f);
}

void updatetarget()
{
    GameObject[] enemies = GameObject.FindGameObjectsWithTag("enemy");
    float shortestdistance = Mathf.Infinity;
    GameObject nearestenemy = null;
    foreach (GameObject enemy in enemies)
    {
        float distanceToenemy = Vector3.Distance(transform.position, enemy.transform.position);
        if (distanceToenemy < shortestdistance)
        {
            shortestdistance = distanceToenemy;
            nearestenemy = enemy;
        }
    }

    if(nearestenemy != null && shortestdistance<=range)
    {
        target = nearestenemy.transform;
    }
    else
    {
        target = null;
    }
}
void Update()
{
    if (target == null)
    {
        return;
    }
    else
    {
        Vector3 dir = target.position-transform.position;
        Quaternion lookrotation = Quaternion.LookRotation(dir);
       //rotation
        Vector3 rotation = Quaternion.Lerp(parttorotate.rotation, lookrotation, 
        rotationspeed*Time.deltaTime).eulerAngles;
        parttorotate.rotation = Quaternion.Euler(-90f,0f, rotation.y);
       //-90 on X is because of my model, I think I designed it wrong in blender and now axis are not okay XD
    }
}

and video I’ve been following:

2

I think this line does not correct.
Since you want it to rotate around Y axis, it should be

parttorotate.rotation = Quaternion.Euler(-90f, rotation.y, 0f);