What I did: Right-clicked on the Task Manager, click Task Manager Settings, under Grouping and Sorting choose Grouping "By Program Name". Leave "Open Groups in Popups" unchecked. Click 'Apply'. What I expected to happen: I would expect the windows to be grouped by program (eg. all my Atom windows appear as one item in the Task Manager) and clicking on that item would raise just one window of the group. What actually happens: The windows do not group at all. They only group if I check "Open Groups in Popups". This is not desirable behavior because I do not like interacting with the popup menu of windows. Additional info: in addition to making grouping function in the case that 'Open Groups in Popups" is unchecked, it would be ideal if Task Manager had an option here that would make it so that upon clicking a group, the most recently used window in that group would be raised. See: https://bugs.kde.org/show_bug.cgi?id=390400).
They do group, group as in "the buttons stay together". Changing to wishlist for a feature to collapse windows into the same button and clicking them to raise all windows. There has been a wish about allowing to do that on middle click or something like that but the problem was I think restoring the proper stacking order of windows when doing so.
Okay, so there was definitely some confusion on my part re: wording. I would not have thought "group" would mean "the buttons stay together" but I understand now. I think you have it nearly right on what the wishlist item would be, except that rather than having the single button raise all windows, provide an option for it to either raise all windows OR just the most recent window. My guess is that in either case you still need to track and access the stacking order. Thanks!