[Bug]: CreateSession: Portal request didn't succeed: Other on Linux X11 (KDE Plasma) #1491

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Describe the bug

When attempting to start a recording on Linux running KDE Plasma under an X11 session (XDG_SESSION_TYPE=x11), OpenScreen fails immediately after clicking record with the following error notification:
Error: CreateSession: Portal request didn't succeed: Other

The source selection dialog never appears.

Under the hood:
OpenScreen delegates screen capture to org.freedesktop.portal.ScreenCast via xdg-desktop-portal. On KDE Plasma under X11, xdg-desktop-portal-kde does not implement the ScreenCast portal interface (it is only available within KWin on Wayland sessions). As a result, the DBus CreateSession call is rejected by the portal backend.

Expected behavior

1. User Guidance: OpenScreen should gracefully detect that the ScreenCast portal is unavailable or unsupported on the active desktop session and display a clear, actionable message (e.g., "Screen recording on KDE Plasma requires a Wayland session, or switch to an X11-compatible capture method"), instead of an unhandled raw DBus error.
2. Fallback: Ideally, provide a fallback to standard X11 recording (such as x11grab / XGetImage or PipeWire X11 screencast) when XDG_SESSION_TYPE === 'x11'.

To Reproduce

1. Log in to a Linux system running KDE Plasma in an X11 session (XDG_SESSION_TYPE=x11).
2. Open OpenScreen.
3. Click "Record".
4. The system picker never opens; the error toast Error: CreateSession: Portal request didn't succeed: Other appears.

Screenshots

Error: CreateSession: Portal request didn't succeed: Other
(Error notification toast triggered upon clicking 'Record')

OS

Linux

OS Version

Ubuntu 24.04 LTS (KDE Plasma, X11)

Device Type

Laptop

Additional context

• Session: XDG_SESSION_TYPE=x11, XDG_CURRENT_DESKTOP=KDE
• Portal packages present: xdg-desktop-portal, xdg-desktop-portal-kde, xdg-desktop-portal-gtk
• The issue does not occur when switching to a Wayland session (Plasma (Wayland)), where xdg-desktop-portal-kde successfully creates the screencast stream.