SUMMARY If you press Alt+Tab when no windows are open, and release it after a window opens, all windows and panels disappear. STEPS TO REPRODUCE 1. Launch Firefox. For me, it takes about a second before the window appears. 2. Immediately press Alt+Tab and hold Alt. The window switcher will say "Show Desktop". 3. Once Firefox loads, the window switcher will say "Mozilla Firefox". Release Alt. OBSERVED RESULT Everything but the wallpaper and cursor disappears. If you open another Firefox window using Ctrl+N, it's also invisible. Windows can be interacted with, using keyboard or mouse. EXPECTED RESULT Windows don't become all invisible. SOFTWARE/OS VERSIONS Operating System: openSUSE Tumbleweed 20200421 KDE Plasma Version: 5.18.4 KDE Frameworks Version: 5.69.0 Qt Version: 5.14.1 Kernel Version: 5.6.4-1-default OS Type: 64-bit Processors: 4 × Intel® Core™ i5-6200U CPU @ 2.30GHz Memory: 7.6 GiB of RAM ADDITIONAL INFORMATION I think this occurs in both X11 and Wayland.
This still happens in Plasma 5.22.1 on Arch Linux, on X11. Restarting kwin fixes the bug.
This bug was reported against an outdated version of KWin. We have made many changes since the. If the issue persists in newer versions can you reopen the bug report updating the version number.