In order to define the enumerations, you have to add them in an array notation to the default value of the property. It is not necessary to set the values in quotes.
There are different predefined types of buttons in OpenUI5. The properties can be maintained as a list in the widget mask. In our example, we look at all different button types in the OpenUi5 API Reference and transfer them into the widget edit mask with the appropriate syntax:
Result in the UI Designer