Lets you view a scene with even lighting.

FullBrightSceneCamera.cs

using UnityEditor;
using UnityEngine;

namespace Nomnom.Editor {
    public sealed class FullBrightSceneCamera {
        private const string KEY = "key_FullBrightSceneCamera";
        
        private static Transform? _rig = null;
        
        [InitializeOnLoadMethod]
        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]
        private static void OnLoad() {
            HandleState();
            
            SceneView.onSceneGUIDelegate -= OnSceneGUI;
            SceneView.onSceneGUIDelegate += OnSceneGUI;
        }
        
        // togglable editor menu item
        [MenuItem("Tools/Nomnom/Toggle Full Bright Scene Camera")]
        private static void Toggle() {
            var value = !EditorPrefs.GetBool(KEY);
            if (value) {
                Debug.Log("Enabled Full Bright Scene Camera");
            } else {
                Debug.Log("Disabled Full Bright Scene Camera");
            }
            
            EditorPrefs.SetBool(KEY, value);
            HandleState();
            
            SceneView.onSceneGUIDelegate -= OnSceneGUI;
            SceneView.onSceneGUIDelegate += OnSceneGUI;
        }
        
        private static void OnSceneGUI(SceneView sceneview) {
            HandleState();
        }

        private static bool GetRigState() {
            var enabled = EditorPrefs.GetBool(KEY) && !EditorApplication.isPlaying;
            var sceneView = GetSceneView();
            if (sceneView is not null && !sceneView.sceneLighting) {
                enabled = false;
            }
            return enabled;
        }

        private static void HandleState() {
            var found = GameObject.FindWithTag("EDITOR_RIG");
            if (!found && GetRigState()) {
                CreateRig();
            }
            
            if (!_rig && found) {
                _rig = found.transform;
            }

            HandleRigState();
        }

        private static void HandleRigState() {
            if (!_rig) return;
            if (!GetRigState()) {
                GameObject.DestroyImmediate(_rig!.gameObject);
                Debug.Log("Destroyed UnlitRig");
            }
        }

        private static SceneView? GetSceneView() {
            var sceneViews = SceneView.sceneViews;
            var lastActiveSceneView = SceneView.lastActiveSceneView;
            if (lastActiveSceneView is null) {
                if (sceneViews.Count == 0) return null;
                lastActiveSceneView = sceneViews[0] as SceneView;
            }

            if (lastActiveSceneView is null) return null;
            return lastActiveSceneView;
        }

        private static void CreateRig() {
            CreateRig(GetSceneView()?.camera!);
        }

        private static void CreateRig(Camera camera) {
            if (!camera) return;
            
            var rig = new GameObject("UnlitRig");
            rig.tag = "EDITOR_RIG";
            rig.transform.SetParent(camera.transform.parent);
            rig.hideFlags = HideFlags.HideInHierarchy | HideFlags.DontSave;
            var directions = new[] {
                new Vector3(0, 0, 1),
                new Vector3(0, 0, -1),
                new Vector3(1, 0, 0),
                new Vector3(-1, 0, 0),
                new Vector3(0, 1, 0),
                new Vector3(0, -1, 0),
            };
            for (int i = 0; i < 6; i++) {
                var light = new GameObject($"Light{i}");
                light.transform.SetParent(rig.transform);
                light.transform.rotation = Quaternion.LookRotation(directions[i]);
            
                var lightComponent = light.AddComponent<Light>();
                lightComponent.type = LightType.Directional;
                lightComponent.intensity = 0.3f;
            }

            _rig = rig.transform;
            Debug.Log("Created UnlitRig");

            HandleRigState();
        }
    }
}

Will disable automatically when entering play mode, and when scene lighting is turned off.

Toggle the effect via Tools > Nomnom > Toggle Full Bright Scene Camera

Unity_lMcy9G3FOJ.mp4