Created attachment 138694 [details] screenshot SUMMARY I believe that the purpose of this feature is to make the panel opaque when an application is taking up all the available screen space, and this usually it happens when a single window is maximized, but it can also happen when there are two or more dividing the available space. STEPS TO REPRODUCE 1. Open multiple windows and divide them into the available space OBSERVED RESULT the panel remains transparent (see the attachment) EXPECTED RESULT should be opaque SOFTWARE/OS VERSIONS Operating System: Arch Linux KDE Plasma Version: 5.21.90 KDE Frameworks Version: 5.82.0 Qt Version: 5.15.2 Graphics Platform: X11
Yes, this is a known limitation.
*** Bug 446685 has been marked as a duplicate of this bug. ***
*** Bug 447043 has been marked as a duplicate of this bug. ***
*** Bug 457000 has been marked as a duplicate of this bug. ***
This has been implemented for Plasma 5.27! Now the panel becomes opaque when any window touches it for any reason.