MouseLookAt.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MouseLookAt : MonoBehaviour
{
    // if your character is rotating but off a fixed angle, adjust this value, likely will be 90 or -90 (degrees)
    [SerializeField] int angleOffset;

    // Update is called once per frame
    void Update()
    {
        var dir = Input.mousePosition - Camera.main.WorldToScreenPoint(transform.position);
        var angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg + angleOffset;
        transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);
    }
}