.twbx
The .twbx contains all of the necessary information to build the visualization along with the data source. This is called a packaged workbook, and it compresses the package of files altogether.
.twb
The .twb contains instructions about how to interact with the data source. When it's building a visualization, Tableau will look at the data source and then build the visualization with an extract. It can’t be shared alone as it contains only instructions, and the data source needs to be attached separately.
