Works for me with Qt 6.5.2, so this may be a Qt 6.6 bug.

Can you do the following:
1. Open a terminal app like Konsole
2. Run `journalctl --follow --user --unit=plasma-kwin_11.service`
3. Make the bug happen again
4. In your terminal issue hit ctrl+c
5. Copy-and-paste the text that appeared there into a comment here

Also, can you see if it works in the Plasma Wayland session?

Thanks!

Hello,
in the live system:

neon@neon:~$ journalctl --follow --user --unit=plasma-kwin_11.service
No journal files were found.

and it report nothing after pressing CTRL+C.

I tried to run the normal journalctl command and extract the last lines hoping they can be related to this problem:

                                             Found module libKF6KCMUtilsQuick.so.6 with build-id: ed5de2ecdce02e8ad648943980a1f896616db92b
                                             Found module libc.so.6 with build-id: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d
                                             Found module libstdc++.so.6 with build-id: e37fe1a879783838de78cbc8c80621fa685d58a2
                                             Found module libQt6Core.so.6 with build-id: 08c2bf4a3137fb207d8c2eab010e710ad83d08f7
                                             Found module libQt6Gui.so.6 with build-id: ff231ad4c87b31a16e318cf3d31d579be167402e
                                             Found module libQt6Widgets.so.6 with build-id: f98b64af32f71e128704a8a5ec5fd954f46b4572
                                             Found module libKF6WidgetsAddons.so.6 with build-id: 419d7d2fd3270acf1aff71a67c345d22750914bc
                                             Found module libKF6I18n.so.6 with build-id: 9c8424ce2aad204c2f1da72dedb15357b387c25c
                                             Found module libKF6CoreAddons.so.6 with build-id: 4b6ab8cd3d2b1b199a0777eb93185a7fa82b585b
                                             Found module libKF6KCMUtilsCore.so.6 with build-id: 997298468518727ff4db0328cb050925eb669801
                                             Found module libKF6Activities.so.6 with build-id: 6adf98aeff81a232fbcdeafb3a615f823d339035
                                             Found module libKF6KCMUtils.so.6 with build-id: 3e0bd8c7d1bae3fa4208c3f220377cda168bc102
                                             Found module kcmshell6 with build-id: e4746f7e4e30e2fad1adda95a027bbda81a7669f
                                             Stack trace of thread 3410:
                                             #0  0x00007fa7c9077a7c __pthread_kill_implementation (libc.so.6 + 0x96a7c)
                                             #1  0x00007fa7c9023476 __GI_raise (libc.so.6 + 0x42476)
                                             #2  0x00007fa7c90097f3 __GI_abort (libc.so.6 + 0x287f3)
                                             #3  0x00007fa7c94ee172 _Z6qAbortv (libQt6Core.so.6 + 0xb9172)
                                             #4  0x00007fa7c94ef0f7 _ZNK14QMessageLogger5fatalEPKcz (libQt6Core.so.6 + 0xba0f7)
                                             #5  0x00007fa7c9af48b7 n/a (libQt6Gui.so.6 + 0x1258b7)
                                             #6  0x00007fa7c9b7ef10 _ZN22QGuiApplicationPrivate25createPlatformIntegrationEv (libQt6Gui.so.6 + 0x1aff10)
                                             #7  0x00007fa7c9b7fb18 _ZN22QGuiApplicationPrivate21createEventDispatcherEv (libQt6Gui.so.6 + 0x1b0b18)
                                             #8  0x00007fa7c9596947 _ZN23QCoreApplicationPrivate4initEv (libQt6Core.so.6 + 0x161947)
                                             #9  0x00007fa7c9b82254 _ZN22QGuiApplicationPrivate4initEv (libQt6Gui.so.6 + 0x1b3254)
                                             #10 0x00007fa7ca33b21d _ZN19QApplicationPrivate4initEv (libQt6Widgets.so.6 + 0x18f21d)
                                             #11 0x000055f2fe67e318 n/a (kcmshell6 + 0x6318)
                                             #12 0x00007fa7c900ad90 __libc_start_call_main (libc.so.6 + 0x29d90)
                                             #13 0x00007fa7c900ae40 __libc_start_main_impl (libc.so.6 + 0x29e40)
                                             #14 0x000055f2fe680905 n/a (kcmshell6 + 0x8905)
                                             
                                             Stack trace of thread 3411:
                                             #0  0x00007fa7c90f9d7f __GI___poll (libc.so.6 + 0x118d7f)
                                             #1  0x00007fa7c7cfd1f6 n/a (libglib-2.0.so.0 + 0xab1f6)
                                             #2  0x00007fa7c7ca53e3 g_main_context_iteration (libglib-2.0.so.0 + 0x533e3)
                                             #3  0x00007fa7c97eb01e _ZN20QEventDispatcherGlib13processEventsE6QFlagsIN10QEventLoop17ProcessEventsFlagEE (libQt6Core.so.6 + 0x3b601e)
                                             #4  0x00007fa7c959c053 _ZN10QEventLoop4execE6QFlagsINS_17ProcessEventsFlagEE (libQt6Core.so.6 + 0x167053)
                                             #5  0x00007fa7c9679150 _ZN7QThread4execEv (libQt6Core.so.6 + 0x244150)
                                             #6  0x00007fa7c809dd4e n/a (libQt6DBus.so.6 + 0x35d4e)
                                             #7  0x00007fa7c970401c n/a (libQt6Core.so.6 + 0x2cf01c)
                                             #8  0x00007fa7c9075b43 start_thread (libc.so.6 + 0x94b43)
                                             #9  0x00007fa7c9107a00 __clone3 (libc.so.6 + 0x126a00)
Sep 13 18:33:07 neon systemd[1]: systemd-coredump@4-3412-0.service: Deactivated successfully.
Sep 13 18:33:07 neon drkonqi-coredump-processor[3414]: "/usr/bin/kcmshell6" 3410 "/var/lib/systemd/coredump/core.kcmshell6.999.c1939ece62d248279ffa764f8440100d.3410.1694629987000000.zst"
Sep 13 18:33:07 neon systemd[1]: drkonqi-coredump-processor@4-3412-0.service: Deactivated successfully.
Sep 13 18:33:07 neon systemd[1673]: Started Launch DrKonqi for a systemd-coredump crash (PID 3414/UID 0).
Sep 13 18:33:07 neon drkonqi-coredump-launcher[3421]: Unable to find file for pid 3410 expected at "kcrash-metadata/3410.ini"
Sep 13 18:33:07 neon drkonqi-coredump-launcher[3421]: QFile::remove: Empty or null file name
Sep 13 18:33:07 neon drkonqi-coredump-launcher[3421]: Nothing handled the dump :O

I may try on wayland, but I need to install neon on a spare hard disk if there is no way to run wayland from the live iso.
Please let me know if the errors above are what you are looking for or they are not relevant.

On my neon unstable, I can reproduce on X11, but cannot on Wayland.

Enrico, is that true for you as well?

(In reply to Nate Graham from comment #4)
> Enrico, is that true for you as well?

I can't install Neon because of bug 474501. I'll try in a Wayland session as soon as I can install Neon

Hello, I've installed Neon (20230920) and... now it works. Both on X11 and Wayland, the windows open up correctly

Patrick, can you please check if you still see this bug on X11 or it's solved for you too?

It's fixed on my system too.

Great!