UPDATE: Moved question to ArcGIS Pro SDK and mentioning Uma Harano as the author of the embedded toolbox article.
I'm following the instructions to embed a toolbox in arcgis pro here, but am getting mixed results. In Visual Studio I've created the esriAddinX with the .tbx, and after starting Pro I can see it has correctly extracted the toolbox into %LocalAppData%\ESRI\ArcGISPro\Toolboxes\GUID\. So far so good.
I'm expecting to see my addin's toolbox listed in Pro's system Geoprocessing toolboxes as per instruction 13 in the guide, but I don't. What am I missing? I've verified that the extracted toolbox is good, and I've populated everything in the .tbx like alias, name, description, etc.
I haven't tried a python toolbox because I want to have toolsets, but if someone knows the .pyt works, then please let me know and I'll go with that. Any ideas/samples will be greatly appreciated. I'm using ArcGIS Pro 2.4.1.
This screenshot is attempting to show the esriAddinX contents being correctly extracted.