The panel looks very beautiful while floating. The slight blur and and the floating popups are very nice.
However, when a window is maximised, the panel smoothly transitions to the pre-Plasma 6 style, occupying all edges. Perfect behaviour.
However, in doing so it loses its transparency/blur effect. The floating popups are also no longer floating. I think it would make sense to keep the transparency intact even when a window is maximised. And the popups should also be floating.