Why can't I limit FPS inside Unity editor?

I have an Unity app that requires a stable fps in editor. The fps itself is really high anywhere from 200 to 280 the problem is that is not consistent. I tried to limit it with the code belove but it still goes up and down too much. So it is not a problem of how high it is but how stable it is. I did not test it in the build because I don't need to build this application I need it to work in editor.

 using UnityEngine; [ExecuteInEditMode] public class FrameRateLimiter : MonoBehaviour { [SerializeField] private int _target = 240; private void Start() { QualitySettings.vSyncCount = 0; } private void Update() { if (Application.targetFrameRate != _target) Application.targetFrameRate = _target; } }