If you have problems with fullscreen applications flickering when desktop effects are enabled then you can try the following solution, which was suggested in KDE Bug 177495:
- Press Alt+F2 and run:
kwriteconfig --file kwinrc --group Compositing --key UnredirectFullscreen --type bool false
- Apply the changes by pressing Alt+F2 and running:
qdbus org.kde.kwin /KWin reconfigure
This forces KWin not to use window unredirection but can affect performance of fullscreen OpenGL applications when desktop effects are enabled. Desktop effects can be suspended to prevent performance issues (press Alt+Shift+F12) before running such applications.