When window borders are hidden by clicking on the title bar of a window, a message box appears that this situation can only be changed by pressing Alt+F3. However, users might forget this combination or VirtualBox might eat up Alt+F3. It would be helpful if window borders could be enabled from the task bar, too.
Yeah, this seems sensible. It's too late for 5.9, but possibly 5.10.
Enable makes sense, I don't see a use-case for disabling though.
Well it'd probably be a toggle action like in the kwin menu.
*** Bug 384325 has been marked as a duplicate of this bug. ***
We could get this as a part of implementing all missing actions only present in the KWin window decoration menu, which is tracked by Bug 360297. *** This bug has been marked as a duplicate of bug 360297 ***