Allow toggling gizmos and selection highlights via hotkey in the Unity Editor.

AnnotationUtilityEx.cs

using System.Reflection;
using static System.Reflection.BindingFlags;
using UnityEditor;
using UnityEditor.ShortcutManagement;

//https://github.com/Unity-Technologies/UnityCsReference/blob/e740821767d2290238ea7954457333f06e952bad/Editor/Mono/Annotation/AnnotationUtility.bindings.cs
public static class AnnotationUtilityEx
{
	[MenuItem("Tools/Editor/Toggle Gizmos & Selection Highlight"), Shortcut("Toggle Gizmos & Selection Highlight", UnityEngine.KeyCode.Space, ShortcutModifiers.Control)]
	public static void ToggleSelectionOutlinesAndGizmos()
	{
		if(ShowSelectionOutline || ShowSelectionWire)
		{
			EditorPrefs.SetBool("showSelectionOutline", ShowSelectionOutline);
			EditorPrefs.SetBool("showSelectionWire", ShowSelectionWire);
			EditorPrefs.SetBool("drawGizmos", SceneView.lastActiveSceneView.drawGizmos);

			SceneView.lastActiveSceneView.drawGizmos = false;
			ShowSelectionOutline = false;
			ShowSelectionWire = false;
		}
		else
		{
			SceneView.lastActiveSceneView.drawGizmos = EditorPrefs.GetBool("drawGizmos");
			ShowSelectionOutline = EditorPrefs.GetBool("showSelectionOutline");
			ShowSelectionWire = EditorPrefs.GetBool("showSelectionWire");
		}
	}
	[Shortcut("Toggle Gizmos", UnityEngine.KeyCode.G)]
	public static void ToggleGizmos()
	{
		SceneView.lastActiveSceneView.drawGizmos = !SceneView.lastActiveSceneView.drawGizmos;
	}

	public static bool ShowSelectionOutline
	{
		get
		{
			if(_showSelectionOutline == null)
				_showSelectionOutline = AnnotationUtility.GetProperty("showSelectionOutline", Static | NonPublic);
			return (bool)_showSelectionOutline.GetValue(null);
		}
		set
		{
			if(_showSelectionOutline == null)
				_showSelectionOutline = AnnotationUtility.GetProperty("showSelectionOutline", Static | NonPublic);
			_showSelectionOutline.SetValue(null, value);
		}
	}
	static PropertyInfo _showSelectionOutline;

	public static bool ShowSelectionWire
	{
		get
		{
			if(_showSelectionWire == null)
				_showSelectionWire = AnnotationUtility.GetProperty("showSelectionWire", Static | NonPublic);
			return (bool)_showSelectionWire.GetValue(null);
		}
		set
		{
			if(_showSelectionWire == null)
				_showSelectionWire = AnnotationUtility.GetProperty("showSelectionWire", Static | NonPublic);
			_showSelectionWire.SetValue(null, value);
		}
	}
	static PropertyInfo _showSelectionWire;

	static System.Type AnnotationUtility
	{
		get
		{
			if(_annotationUtility == null)
			{
				var assembly = typeof(SceneViewCameraWindow).Assembly;
				_annotationUtility = assembly.GetType("UnityEditor.AnnotationUtility");
			}
			return _annotationUtility;
		}
	}
	static System.Type _annotationUtility;
}