This sample shows how to create an EEAddin for the legacy native debugger (the debugger that shipped with Visual Studio 2002 through Visual Studio 2010).
The recomended way to run custom code to format types is by implementing IDkmCustomVisualizer. You can find a sample for this in the ConcordExtensibility repo.
Legacy EE Addins can still be used with Visual Studio's current debugger. But as of Visual Studio 2019 they will no longer work with Visual Studio in the default configuartion.