Adds a UI element to the Unity 2022.1 toolbar using reflection.

AddButtonToUnityToolbar.cs

var toolbarType = Assembly
    .GetCallingAssembly()
    .GetType("UnityEditor.Toolbar")!;

var toolbar = toolbarType
    .GetField("get", BindingFlags.Public | BindingFlags.Static)!
    .GetValue(null);

var toolbarRootVisualElement = toolbarType
    .GetField("m_Root", BindingFlags.Instance | BindingFlags.NonPublic)!
    .GetValue(toolbar) as VisualElement;

var rightToolbar = toolbarRootVisualElement.Q("ToolbarZoneRightAlign");

rightToolbar.Add(new EditorToolbarButton(() =>
{
    Debug.Log("Clicked!");
}) { text = "Click Me" });