KWin crashes on startup on KDE Neon developer edition

[David Hurka]

Hi,

my desktop computer, which runs KDE Neon developer edition, is broken. :(
I don’t know where exactly I should report this.

KWin seems to crash at startup, and I see a small borderless window saying:

> KWin in unstable.
> It seems to have crashed several times in a row.
> You can select another window manager to run:
> (x) kwin_x11
> [OK] [Cancel]

The window returns at click on OK and disappears on Cancel.
Besides this window, there is only black and the mouse cursor.

Because I use automatic login, I can’t tell whether KWin crashes before or 
after login, I guess after.

This issue started after the last update (via aptitude).
I updated again via aptitude and SSH, no change.
I tried to undo the update, but the older packages are no longer available.

I tried to start various applications via SSH -X, and most of them crash with 
the following:

> Cannot mix incompatible Qt library (5.15.3) with this library (5.15.4)
> 21 -- exe=/usr/bin/dolphin
> 13 -- platform=xcb
> 23 -- display=localhost:11.0
> 16 -- appname=dolphin
> 17 -- apppath=/usr/bin
> 9 -- signal=6
> 10 -- pid=64943
> 20 -- appversion=22.07.70
> 20 -- programname=Dolphin
> 31 -- bugaddress=submit at bugs.kde.org
> 12 -- startupid=0
> KCrash: crashing... crashRecursionCounter = 2
> KCrash: Application Name = dolphin path = /usr/bin pid = 64943
> KCrash: Arguments: /usr/bin/dolphin 
> KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi

The first line looks most interesting to me.
I have libqt5core5a 5.15.2+p20.04+tunstable+git20200516.1232-0 installed.
It is the only version known to aptitude.
I think this is what counts as Qt 5.15.3, because of the KDE patch collection 
story.

I have dolphin 4:22.04.0+p20.04+tunstable+git20220420.0015-0 installed.
Again, only available version.

Is it possible that KDE Neon packages were compiled against Qt 5.15.4 
(whatever that means), but ships still Qt 5.15.3?

Or, because dolphin starts with 22.04.0:
Did packages for Ubuntu 22.04 and 20.04 somehow mix in KDE Neon?
I didn’t yet observe KDE Neon to upgrade to Ubuntu 22.04.
(I think no, it’s just the KDE Gear version probably?)

I can not investigate further right now.
If the issue automagically fixes with a future update, I will tell you.

Cheers, David