This would be useful and convenient if you're looking at images/videos from different folders in sequence.

This seems like an intuitively quite plausible idea, thanks! I assume you mean in the tooltip that shows the thumbnails, and by "most focused" you mean the one that is currently focused, not tracking some frequency of how often a user focused a particular window? 

On the other hand, one could argue that a) the first windows are likely the more important ones and b) the usefulness of the popup is highest if the currently active window is not among them, because switching to it doesn't do anything, so on smaller screens a good amount of the limited screen space for displaying the thumbnail list is wasted on a useless option.


Another thing to consider is that media player buttons will only show on the first window (unless we can relatively cleanly identify which particular window is doing the actual playing). So if a user has e.g. multiple browser windows open and there's a video playing in one of them, this would increase the chances that the media player controls are not on screen, reducing their usefulness somewhat. 

I'm still inclined to think it's probably worth it; if the user browses the list and selects one of them, it would make sense to me to start from approximately that position if the user hovers the icon again. Will need to see it in practice though, and maybe get feedback from users who use the thumbnail version (I have the thumbnails disabled myself).

I used "most focused" because it's possible to have multiple windows maximized, while only the one in the front is interactable, that would be the "most focused window".

Admittedly, this is only useful if you're checking each window top-to-bottom, so this feature would work as a page marker.

JFYI the "efficiency" keyword refers to power efficiency, not personal workflow efficiency.

A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/2839