Unity Dropdown - can't render unity dropdown option list in world space

I have a Unity dropdown that is child of a canvas whose render mode set to world space. All elements in this canvas are rendered correctly in world space, except for the dropdown option list that shows up when the user clicks on a dropdown header. This dropdown option list has its own canvas as a component in the inspector, and is a child object of my dropdown menu. Thus, it is supposed to inherit the render mode from it's parent canvas if I understood the Unity manual correctly ("A nested Canvas uses the same Render Mode as its parent. - https://docs.unity3d.com/Packages/com.unity.ugui@1.0/manual/class-Canvas.html").

However, in the game window, the dropdown option list is always rendered in screen space and not as expected in world space. It is shown correctly in world space in my editor window, though. All user interactions with the dropdown list are detected like it was rendered correctly in world space, so I think the issue is only that the rendering is wrong in the game window. Anybody who could give me some advices on how to render my dropdown option list in world space?

Thank you!