I made the switch from kubuntu (focal) to Neon(focal) and now I get log entries such as these :

Aug 19 12:26:36 linux-desktop kwin_x11[1456]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 32379, resource id: 56623148, major code: 18 (ChangeProperty), minor code: 0

Aug 19 12:26:32 linux-desktop kwin_x11[1456]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 31185, resource id: 14682229, major code: 3 (GetWindowAttributes), minor code: 0

Aug 19 12:26:32 linux-desktop kwin_x11[1456]: qt.qpa.xcb: QXcbConnection: XCB error: 9 (BadDrawable), sequence: 31186, resource id: 14682229, major code: 14 (GetGeometry), minor code: 0

I did not see these on Kubuntu .

It seems that every app I start / stop causes some to appear .

Is this some sort of debug that can be turned off ?

I searched and found a way to suppress these messages . Create a file '/usr/share/qt5/qtlogging.ini' and put the following lines in:

[Rules]
*.debug=false
qt.qpa.xcb.xcberror.warning=false
qt.qpa.xcb.xcberror.error=false
qt.qpa.xcb.warning=false
qt.qpa.xcb.error=false
qt.qpa.xcb=false

It seems the errors/warnings I was seeing were harmless (other than lots of log entries) but I would prefer not to see them .

Obviously if you are having qt issues you probably dont want to do this as it may suppress valuable info needed for bug reports