ExcelAddinHelloWorld

https://docs.microsoft.com/en-us/visualstudio/vsto/walkthrough-creating-your-first-vsto-add-in-for-excel

Make sure VSTO is installed for Visual Studio

How to add new Ribbon to addin project

Project -> Add New Item -> Ribbon (Visual Designer)

How to add a new RibbonButton to the Ribbon Ribbon (Visual Designer)

Open the Ribbon (Visual Designer) object
Open the controls toolbox
Expand the Office Ribbon Controls tab
Drag a Button onto the Ribbon