I’m making a progress bar in unity for loading scenes but the bar goes from 0 to 100 without stopping in the middle

public void Loading(string sceneID)
{
    screen.SetActive(true);
    StartCoroutine(LoadingAsync(sceneID));
}

public IEnumerator LoadingAsync(string sceneID)
{
    yield return null;

    AsyncOperation operation = SceneManager.LoadSceneAsync(sceneID);
    operation.allowSceneActivation = false;
    
    while (!operation.isDone)
    {
        float progress = Mathf.Clamp01(operation.progress / .9f);
        Debug.Log(progress * 100 + "%");
        loadingBar.value = progress * 100f;
        loadingPer.text = progress * 100f + "%";
        


        if (operation.progress >= .9f) { operation.allowSceneActivation = true; }

        yield return null;
    }

}

Here is the debug

Expected the loading bar progress to be smooth but it just goes from 0 to 100