CSHARP

look rotation only on y axis in unity

        var dir = PlayerMovement.playerTransform.position - transform.position;
        Quaternion LookAtRotation = Quaternion.LookRotation(dir);

        Quaternion LookAtRotationOnly_Y = Quaternion.Euler(transform.rotation.eulerAngles.x, LookAtRotation.eulerAngles.y, transform.rotation.eulerAngles.z);
        transform.rotation = LookAtRotationOnly_Y;

unity rotate around axis

transform.Rotate(axis, degrees);

Unity Object rotation along any axis

using UnityEngine;
public class Rotation : MonoBehaviour
{
    public float xAngle, yAngle, zAngle;

    public GameObject objectToRotate;

    void Awake()
    {
   //change position here to see object as want
        objectToRotate.transform.position = new Vector3(0.1f, 0.0f, 0.0f);
        objectToRotate.transform.Rotate(90.0f, 0.0f, 0.0f, Space.Self);

    }

    void Update()
    {
        objectToRotate.transform.Rotate(xAngle, yAngle, zAngle, Space.Self);
     
    }
}