Improved GlobalVolumeFeature and added custom GUI

Assets/Scripts/Effects/GlobalVolumeFeature.cs

 using UnityEngine.Rendering;
 using UnityEngine.Rendering.Universal;
 
+//[DisallowMultipleRendererFeature] // once not internal, this needs to be here
 public class GlobalVolumeFeature : ScriptableRendererFeature
 {
     class GlobalVolumePass : ScriptableRenderPass
             {
                 var index = QualitySettings.GetQualityLevel();
 
-                if(_qualityProfiles.Count >= index)
-                    qualityVol.sharedProfile = _qualityProfiles?[QualitySettings.GetQualityLevel()];
+                if(_qualityProfiles.Count >= index && _qualityProfiles[index] != null)
+                    qualityVol.sharedProfile = _qualityProfiles?[index];
-
         }
 
         // Here you can implement the rendering logic.
         m_ScriptablePass = new GlobalVolumePass
         {
             // Configures where the render pass should be injected.
-            renderPassEvent = RenderPassEvent.BeforeRendering,
+            renderPassEvent = RenderPassEvent.AfterRenderingTransparents,
             _baseProfile = this._baseProfile,
             _layerMask = this._layerMask,
             _qualityProfiles = this._qualityProfiles,

Assets/Scripts/Editor/GlobalVolumeFeatureEditor.cs

+using System;
+using System.Collections;
+using System.Collections.Generic;
+using UnityEditor;
+using UnityEngine;
+using UnityEngine.Rendering;
+
+[CustomEditor(typeof(GlobalVolumeFeature))]
+public class GlobalVolumeFeatureEditor : Editor
+{
+    private GlobalVolumeFeature feature;
+    private SerializedProperty profileList;
+    private SerializedProperty baseProfile;
+    
+    private static class Styles
+    {
+        public static GUIStyle frameBox = new GUIStyle(EditorStyles.helpBox);
+        public static GUIStyle header = new GUIStyle(EditorStyles.boldLabel);
+
+        public static GUIContent baseGUI = new GUIContent("Global Base Profile",
+            "This Profile is always active and should be treated as a default global settings for Volumes.");
+    }
+
+    private void OnEnable()
+    {
+        profileList = serializedObject.FindProperty(nameof(feature._qualityProfiles));
+        baseProfile = serializedObject.FindProperty(nameof(feature._baseProfile));
+    }
+
+    public override void OnInspectorGUI()
+    {
+        feature = (GlobalVolumeFeature)target;
+
+        EditorGUILayout.PropertyField(baseProfile, Styles.baseGUI);
+        
+        EditorGUILayout.LabelField("Quality Level Profiles", Styles.header);
+        
+        var qualityLevelNames = QualitySettings.names;
+        
+        EditorGUILayout.BeginVertical(Styles.frameBox);
+        // Draw Quality level entries
+        for (var i = 0; i < qualityLevelNames.Length; i++)
+        {
+            if (i >=  feature._qualityProfiles.Count)
+            {
+                feature._qualityProfiles.Add(null);
+                EditorUtility.SetDirty(feature);
+                serializedObject.Update();
+            }
+            EditorGUI.BeginChangeCheck();
+            var obj = feature._qualityProfiles[i];
+            feature._qualityProfiles[i] = (VolumeProfile)EditorGUILayout.ObjectField(qualityLevelNames[i], obj, typeof(VolumeProfile), false);
+            if (EditorGUI.EndChangeCheck())
+            {
+                EditorUtility.SetDirty(feature);
+                serializedObject.Update();
+            }
+        }
+        EditorGUILayout.EndVertical();
+
+        if (qualityLevelNames.Length < feature._qualityProfiles.Count)
+        {
+            feature._qualityProfiles.RemoveRange(qualityLevelNames.Length, feature._qualityProfiles.Count - qualityLevelNames.Length);
+            EditorUtility.SetDirty(feature);
+        }
+    }
+}

Assets/Scripts/Editor/GlobalVolumeFeatureEditor.cs.meta

+fileFormatVersion: 2
+guid: 234cf3565ca2a49dc860867404243203
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: