docs(troubleshooting): Add workaround for "blur" plugin in KDE (#3328)

docs/troubleshooting.md

@@ -165,6 +165,14 @@ high as long as the encoder is used.
 ### Gamescope compatibility
 Some users have reported stuttering issues when streaming games running within Gamescope.
 
+### Occasional flickering in KDE
+
+The `blur` plugin causes flickering during streaming for some people. Disable it from the
+KDE System Settings or from the commandline:
+```bash
+qdbus org.kde.KWin /Effects unloadEffect blur
+```
+
 ## macOS
 
 ### Dynamic session lookup failed