Why doesn't maxDegreesDelta matter in my RotateTowards?

I'm trying to get my gameobject to rotate slower than the input. If I use Quaternion.RotateTowards, it doesn't matter what I put in for maxDegreesDelta (it can be 0, it can be 1000, it can be multiplied by Time.deltaTime or by Time, or by a counter...) The rotation is always exactly as fast as the input. The same thing happens when I use Quaternion.Slerp... time simply doesn't matter. What am I missing?

 using System.Collections;  
 using System.Collections.Generic;  
 using UnityEngine;  
 
 public class cubetest : MonoBehaviour
 {
     Transform destinationRotation;
 
     public float rotationSensitivity = 1;
     public float rotationSpeed = 1;
 
     // Start is called before the first frame update
     void Start()
     {
         destinationRotation = transform;
     }
 
     // Update is called once per frame
     void Update()
     {
         if (Input.GetAxis("Mouse X") != 0)
         {
             destinationRotation.Rotate(0, Input.GetAxis("Mouse X") * rotationSensitivity, 0, Space.World);
         }
 
         transform.rotation = Quaternion.RotateTowards(transform.rotation, destinationRotation.rotation, rotationSpeed * Time.deltaTime);
     }
 }