https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.toolbar.toolbarbuttoncollection.indexofkey?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
ToolBar.ToolBarButtonCollection.IndexOfKey(String) Method (System.Windows.Forms) | Microsoft Learn
Retrieves the index of the first occurrence of a ToolBarButton with the specified key.
windows formstoolbarstringmethodsystem