Only set the config dropdown once rather than every frame as ARKit does not change the current configuration immediately.

Assets/Scripts/CameraConfigController.cs

     void Awake()
     {
         m_Dropdown = GetComponent<Dropdown>();
+        m_Dropdown.ClearOptions();
-    void Update()
+    void PopulateDropdown()
-        m_Dropdown.ClearOptions();
-
         var cameraSubsystem = ARSubsystemManager.cameraSubsystem;
         if (cameraSubsystem == null)
             return;
         if (configurations.count == 0)
             return;
 
-        // Here we demonstrate the two ways to enumerate the camera configurations.
-        // Typically, you would do this once, perhaps at the start of the AR app
-        // rather than every frame.
+        // There are two ways to enumerate the camera configurations.
-        // Here, we use a foreach to iterate over all the available configurations
-        m_ConfigurationNames.Clear();
+        // 1. Use a foreach to iterate over all the available configurations
-        // We can also use a normal for...loop
+        // 2. Use a normal for...loop
         var currentConfig = cameraSubsystem.GetCurrentConfiguration();
         for (int i = 0; i < configurations.count; i++)
         {
         }
+    }
+
+    void Update()
+    {
+        if (m_ConfigurationNames.Count == 0)
+            PopulateDropdown();
     }
 }