The ToolBarButton is missing the ability to set the "aria-label".
When attempting to just add it directly, I get the following error:
Where there is a spacer inside the ToolBar or when there are no items that should be hidden anymore, the overflow anchor overlay with the other items.
#1563693
Use a ToolBar with its ToolBarTemplateItem (with DropDownList inside of the template) in a separate component. Try to switch values in the DropDownList with the arrows of the keyboard. The value in the DropDownList does not change until you move away from it with a right arrow. This only happens when the template with the dropdown inside is in a separated component.
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The workaround for such a scenario is to export the DropDownList too onto a separated component and then call it in the ToolBarTemplateItem. See the attached sample project.