If you set any panel to autohide in KDE, it will make it's area unclickable in fullscreen apps even though it's not shown.
1 Answer
This is a known bug and it wasn't fixed for a long time: https://bugs.kde.org/show_bug.cgi?id=199017
But there is a workaround: Change from "Autohide" to "Allow overlapping" panel behaviour (or whatever is the original string, I use localized version currently). The panel will still show up when you bring pointer to the edge of the screen.