KDE Plasma Wayland black screen after update

[m-bostaurus]

– KWin “Atomic modeset failed: Permission denied” – nvidia and nouveau affected

System:

• Manjaro KDE, Plasma 6.6.4 (updated to 6.6.5 during troubleshooting)
• Kernel: linux618
• GPU: NVIDIA (tested with both video-nvidia-575xx and free video-linux/nouveau driver)
• Two monitors, side by side
• The problem affects two different machines (a desktop and a laptop with only one monitor), so it is not a multi-monitor issue

After a large Manjaro update, both machines boot into a black screen on Plasma Wayland. Only the mouse cursor is visible (and on one machine a clock widget). No taskbar, no wallpaper, no desktop. After roughly 90 seconds the session crashes and SDDM restarts. Plasma X11 has not been tested yet but is the fallback option.

Journal output (key lines):

kwin_wayland: Atomic modeset test failed! Keine Berechtigung
kwin_wayland: Applying output configuration failed!
kwin_wayland: PipeWire remote error: connection error
sddm: Auth: sddm-helper crashed (exit code 1)
plasmashell: Error loading the wallpaper .../at.lehklu.plasma.vallpaper6/...: 
  module "org.kde.plasma.private.pager" is not installed
  module "org.kde.plasma.private.mediaframe" is not installed

What we tried:

• Removed ~/.config/kwinoutputconfig.json → no change
• Added mz-c03 to groups video, render, input → no change
• Verified nvidia-drm.modeset=1 is set in GRUB and /etc/modprobe.d/mhwd-gpu.conf → already correct
• Full system update to Plasma 6.6.5, kwin 6.6.5-2, linux618-nvidia-575xx 575.64.05-39 → no change
• Switched to free video-linux (nouveau) driver → same black screen, so the issue is not nvidia-specific

Suspected cause:

Since the problem occurs on two different machines with different hardware and persists with both proprietary and free drivers, the issue appears to be in KWin or Plasma itself. The “Permission denied” on the atomic modeset call is suspicious – it may be a regression in how KWin or logind handles DRM device access on Wayland after the update. A third-party wallpaper plugin (at.lehklu.plasma.vallpaper6) also fails to load, but this is likely a secondary symptom.

(I am working through this with the help of Claude/Anthropic AI, which has been assisting with log analysis and troubleshooting steps.)

Question:

Has anyone experienced the same issue after a recent Manjaro update? Any hints on what may have changed in KWin 6.6.x regarding DRM/Wayland permissions would be very helpful. Is there a known workaround short of switching to X11?

Mod edit: Fixed formatting; changed blockquote to code.

[m-bostaurus]

That helped:

mv ~/.config/plasma-org.kde.plasma.desktop-appletsrc ~/.config/plasma-org.kde.plasma.desktop-appletsrc.bak

systemctl --user restart plasma-plasmashell

Mod edit: Changed blockquote to code formatting.

[ErinHong]

I’ve seen a few black-screen issues after Plasma updates that turned out to be graphics-driver related. If X11 still works, it might be worth checking the system logs with journalctl -b for any Wayland or GPU errors. That can sometimes point directly to the culprit.

[m-bostaurus]

The reason for the problem was Vallpaper 6.0.3
So I did this to get rid of it:

rm -rf ~/.local/share/plasma/wallpapers/at.lehklu.plasma.vallpaper6

To control:

grep -i vallpaper ~/.config/plasma-org.kde.plasma.desktop-appletsrc

And to save the wanted configuration:

cp ~/.config/plasma-org.kde.plasma.desktop-appletsrc ~/.config/plasma-org.kde.plasma.desktop-appletsrc.$(date +%Y%m%d)

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Mod edit:- Please present all code, commands and command output as pre-formatted text rather than as quoted text. Remedied for you this time. No charge.