Bug 512813

SUMMARY

When I try to choose a screen/window to share in OBS Studio, the dialog doesn't appear at all

The following appears in systemctl --user status plasma-xdg-desktop-portal-kde.service

```
Nov 30 23:01:15 compooter xdg-desktop-portal-kde[40744]: QQmlApplicationEngine failed to load component
Nov 30 23:01:15 compooter xdg-desktop-portal-kde[40744]: qrc:/qt/qml/org/kde/xdgdesktopportal/ScreenChooserDialog.qml:14:1: Type ScreenChooserDialogTemplate unavailable
Nov 30 23:01:15 compooter xdg-desktop-portal-kde[40744]: qrc:/qt/qml/org/kde/xdgdesktopportal/ScreenChooserDialogTemplate.qml:9:1: Type PortalDialog unavailable
Nov 30 23:01:15 compooter xdg-desktop-portal-kde[40744]: qrc:/qt/qml/org/kde/xdgdesktopportal/PortalDialog.qml:328:25: FlexboxLayout is not a type
Nov 30 23:01:15 compooter xdg-desktop-portal-kde[40744]: qt.core.qobject.connect: QObject::connect: Cannot connect (nullptr)::clearSelection() to ScreenChooserDialog::clearSelection()
```

Bisect led to 

```
5b4226088b9997d759d52f6446875ed2529c837f is the first bad commit
commit 5b4226088b9997d759d52f6446875ed2529c837f
Author: Harald Sitter <sitter@kde.org>
Date:   Wed Nov 12 12:50:58 2025 +0100

    portaldialog: support adding items left of the button box
    
    allows us to put contextually relevant options in the footer
    
    OOTB buttonbox doesn't support adding things before the button view so
    we need to turn the entire footer into a control. that better mimics the
    header anyway though.
    
    inside the footerControl we then have a layout with a leftcontainer and
    the buttonbox as right container. for convergence reasons we use the new
    flexboxlayout here so we can transparently reflow things while still
    having layout control WRT filling (something Flow unfortunately doesn't
    do -- alas, flexboxlayout is also not very reliable so equip the
    containers with layout guides)

 src/PortalDialog.qml | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 61 insertions(+), 21 deletions(-)

```

STEPS TO REPRODUCE
1. Install xdg-desktop-portal-kde built at the commit I bisected to or at any point after
2. Try to select a screen/window to share in OBS Studio

OBSERVED RESULT

The screen/window dialog doesn't appear at all

EXPECTED RESULT

The screen/window dialog appears

SOFTWARE/OS VERSIONS
Operating System: Gentoo 2.18
KDE Plasma Version: 6.5.80
KDE Frameworks Version: 6.21.0
Qt Version: 6.9.3
Kernel Version: 6.18.0-rc7 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 7800X3D 8-Core Processor
Memory: 32 GiB of RAM (30.5 GiB usable)
Graphics Processor 1: AMD Radeon RX 6800
Graphics Processor 2: AMD Ryzen 7 7800X3D 8-Core Processor