On the gnome shell with wayland, poupping up position of nested menu seems not correct, when the app is positioned near by the right most position of the screen. Resulting popup position is not like the one we can expect with X. You may refer to the attached screenshot. (Testing app. is a 'menus' example, which can be found among the qt examples)

Anyway, it seems like user experiences from nested menu is not good enough, because menu could be cropped out into the right or hide parent menu item it was trigged.

It would be nice if this behavior could be equal with the one we can see with X.