Flatpak new UI cannot take screenshots on Ubuntu 24.04 LTS

Flatpak new UI cannot take screenshots on Ubuntu 24.04 LTS KDE/Wayland because KDE portal on LTS lacks required Screenshot method, and UI also gives misleading “must be installed system-wide” message

Environment

OS: Ubuntu Studio 24.04 LTS (Noble)

Desktop: KDE Plasma 5.27.11

Session: Wayland

GPU: AMD

App: com.dec05eba.gpu_screen_recorder (Flatpak, installed system-wide)

xdg-desktop-portal: 1.18.4-1ubuntu2.24.04.1

xdg-desktop-portal-kde: 5.27.11-0ubuntu3

Summary
On Ubuntu 24.04 LTS with KDE Plasma Wayland, the new Flatpak UI cannot take screenshots and reports:

Failed to take a screenshot. Verify if settings are correct

At the same time, the app may also incorrectly report that GPU Screen Recorder must be installed system-wide even when it already is installed system-wide.

This appears to be caused by the Flatpak UI assuming a newer KDE portal/Screenshot API than what is available on Ubuntu 24.04 LTS, instead of correctly detecting and handling the LTS KDE portal version.

Expected behavior

If the required screenshot portal API is unavailable on the current host KDE portal version, the app should detect that correctly and show a precise message such as:

screenshot capture is unavailable on this KDE portal version

or fallback to another supported path if possible

The app should not display the “must be installed system-wide” warning when the Flatpak is already installed system-wide.

The app should explicitly handle Ubuntu 24.04 LTS / KDE Plasma 5.27 portal limitations, since this is a major LTS target.

Actual behavior

New UI screenshot capture fails with:

Failed to take a screenshot. Verify if settings are correct

The app may incorrectly show:

GPU Screen Recorder needs to be installed system-wide to use the new UI
even though it is already installed system-wide.

This makes the new UI partially unusable on a common LTS KDE setup.

Relevant checks already performed

Flatpak permissions:

[Context]
shared=network;ipc;
sockets=x11;wayland;pulseaudio;session-bus;fallback-x11;
devices=dri;all;shm;
features=per-app-dev-shm;
filesystems=xdg-run/pipewire-0;/dev/input;/dev/uinput;xdg-videos;xdg-pictures;

[Session Bus Policy]
org.freedesktop.Flatpak=talk
org.kde.StatusNotifierWatcher=talk
org.kde.KWin=talk

[Environment]
GSR_NO_UINPUT=1

Installed portal packages:

xdg-desktop-portal-gtk 1.15.1-1build2
xdg-desktop-portal-kde 5.27.11-0ubuntu3
xdg-desktop-portal-lxqt 0.5.0-0ubuntu6
xdg-desktop-portal 1.18.4-1ubuntu2.24.04.1

Portal screenshot method test:

gdbus call --session \
--dest org.freedesktop.portal.Desktop \
--object-path /org/freedesktop/portal/desktop \
--method org.freedesktop.portal.Screenshot.TakeScreenshot

Result:

Error: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod:
No such method “TakeScreenshot”

This strongly suggests the host KDE portal on Ubuntu 24.04 LTS does not provide the Screenshot method expected by the new UI.

Why this matters
Ubuntu 24.04 LTS + KDE Plasma is a very common long-term-supported Linux target. The Flatpak app should not assume newer KDE portal capabilities without:

proper runtime detection

clear error reporting

or fallback behavior

Suggested fix

Detect screenshot portal capability explicitly before attempting to use it.

If org.freedesktop.portal.Screenshot.TakeScreenshot is unavailable:

show an accurate compatibility message

avoid generic “verify settings” messaging

Fix the system-wide install detection logic so it does not falsely report that requirement when already installed via flatpak install --system.

Consider special-casing or documenting Ubuntu 24.04 LTS / KDE Plasma 5.27 limitations in the new UI.

Optional enhancement
A compatibility matrix in docs or runtime checks for:

KDE Plasma 5.27 LTS

Ubuntu 24.04 LTS

Wayland + Flatpak
would save users a lot of time.

Thanks.