Consistently reproducible on X11.

STEPS TO REPRODUCE
1. Create two Firefox [profiles](https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles).
2. Launch one of them, and open two tabs in a window.
3. Drag&drop one tab in order to detach in, creating a new window.

At this point, trigger either the Overview effect or the Grid effect. Notice that there is a small white/dark spot (light/dark theme) that "behaves" like a small window in the effect. For example, in the Overview, you can hover over it, and a blue border will appear around it, at which point you can select it. Selecting it, will crash KWin.

Continuing from the last step, (without closing the first running instance/profile of Firefox):

4. Launch Firefox using the second profile.
5. Again, open two tabs and detach one of them, like in step 3.
6. Try to trigger either the Overview or the Grid effect.

At this point, triggering the effect causes KWin to crash immediately.


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Archlinux
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0

ADDITIONAL INFORMATION

Bisection result:

fc3a2d0d5d39c3003c2909580bf2c38a1dc6ba1f is the first bad commit
commit fc3a2d0d5d39c3003c2909580bf2c38a1dc6ba1f
Author: Yifan Zhu <fanzhuyifan@gmail.com>
Date:   Thu Apr 11 09:31:03 2024 -0700

    scripting/windowmodel: match screen closest to center for filter
    
    When filtering windows by screen, match the screen closest to the window
    center, instead of testing whether the window is visible on the current
    screen. The new method guarantees that when filtering by screen, the
    window appears for exactly one screen. Previously windows spanning
    multiple screens appear on all of them, and off-screen windows are not
    shown in any screen.
    
    BUG: 480028
    BUG: 485337
    
    FIXED-IN: 6.0.4
    
    
    (cherry picked from commit 1a4606d990b89f403e048edef4b07b407b94a370)

 src/scripting/windowmodel.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)