If you want to insert more elements in a row to your diagram, select a tool you want to use (e.g. UML class) from the toolbox. Then click second time on the selected tool button to lock this tool. You will see a small lock icon on the tool button. Now each click on the diagram canvas creates a new element (e.g. UML class). It's easy and quick.
Insert Elements on Single Click
Tutorials| 26 October 2018 | Dusan Rodina - softwareideas.net
You can add several elements to your diagram very easily on single click.