Try removing and re-adding the ESRI references, make sure 'embed interop types' is set to false for each ESRI assembly.
Note that this is the Pro SDK forum, you may get more responses in the ArcObjects forum in future.
I created a new add-in using the ArcObjects SDK 10.6. I used the VB 'ArcMap Add-in' Project Template wizard to create a new add-in by selecting a button on the pop-up wizard. When I built the application everything worked as expected. You should check if your references are resolved properly - here is my screen with the config.designer.vb file and the references in the solution explorer. Again as Sean mentioned, this is the wrong forum for your ArcObjects question.