this affects the ‘Task Manager’ task bar
what was: clicking on a pinned app would open the window, display the task bar entry, and hide the pinned icon
what is: clicking on a pinned app no longer hides the pinned icon
i much preferred the former behavior
That has never been the case.
Left-clicking on a pinned application would open the application if it was not already running, and instead of hiding the icon, it would highlight the icon. The method for highlighting depends on the chosen Plasma theme — in the Breath or Breeze styles for instance, there would be a colored bar above the icon. If you have more than one running instance of the application, there will also be an indicator of such on the icon.
Left-clicking an already open application’s icon would by default activate said application’s window, and if you left-click it while the window is already active, it would by default minimize the window, in which case the icon on the task bar would still be highlighted, but in a different way — for instance, a subtle shade, again depending on the Plasma style.
Applications whose icon disappears from the task bar probably have a window rule set for them. If you had any existing window rules from before the migration to Plasma 6, then you may need to revise and update them.
it was and it was independent of window rules
again, this is regarding specifically the ‘Task Manager’ task bar, not the default icons only task bar
clicking a pinned icon would open the app and place the normal, elongated task bar button in the task bar and hide the pinned icon while the window was running, pretty much exactly as if the ‘Keep launchers separate’ option is disabled, however the task bar button would be positioned to the right of any other buttons for running programs rather than replacing the pinned icon
i’m aware of that option, however that doesn’t result in the desired behavior
in other words, i much preferred the button to be placed to the right of any other running windows rather than between other pinned icons
I’m confused 
First you wanted:
what was: clicking on a pinned app would open the window, display the task bar entry, and hide the pinned icon
what is: clicking on a pinned app no longer hides the pinned icon
i much preferred the former behavior
Then you wanted:
sorry for the confusion - what i want hasn’t changed - i just didn’t fully explain it in the opening post
what i want is the window button to be placed to the right of any other running windows rather than between other pinned (launcher) icons AND the launcher icon to be hidden while the window is running … exactly as how it worked in plasma 5
Disable “Keep launchers separate”
Then set Sort to “Do not sort”
And force new task to appear to left
I think this would be the exact opposite of what he wants to accomplish. Sorting should be set to “manual”, and “keep launchers separate” should be enabled.
Manual sort will launch the app in the position of its pinned icon, for example opened Kate
Enabling “Keep launchers separate” will retain the pinned icon, for example opened Kate
Then I guess it must be a bug. 
It works as expected, “Keep launchers separate” means that those pinned icons shouldn’t disappear when you click on them, so another new entry will be created for the newly opened app.
If you disable “Keep launchers separate”, then clicking on Kate pinned icon will make it disappear, and it will be replaced by the newly created Kate entry
that’s almost exactly what i’m after, except the task bar window buttons cannot be re-ordered (‘do not sort’), whereas in plasma 5 they could
so to be complete, in 5 you could set sort to manual, enable ‘keep launchers separate’, ‘do not group’ and then when clicking a launcher, the icon would disappear and a normal window button would be added to the right of any existing window buttons, and they could be manually rearranged
there is a bug here i think - in order to disable ‘keep launchers separate’, the sort option has to be set to manual first, then to ‘do not sort’ - if that isn’t done then the launcher icon remains after it’s clicked
There are many such bugs in Plasma 6 that I myself have encountered here as well, along the lines of “first you have to do this, then switch back to that, and then it works”. So feel free to file a bug report about this particular issue at bugs.kde.org. 
