Created attachment 189808 [details] recording of the issue SUMMARY Starting from Plasma 6.6, GTK applications don't correctly change their color scheme in response to changing system theme; instead they seem to change their color scheme to the previous value of system theme. E.g. if I'm in light mode and change system theme to Breeze Dark, GTK applications will stay in light mode; if I then change system theme to Breeze (light), GTK applications will turn into dark mode. Closing and reopening the GTK application makes it launch in the correct mode (until the next theme change). It's somewhat difficult to accurately describe the behavior, so I attached a recording of the issue. It shows 2 non-GTK applications (Kate and LibreOffice) responding correctly to system theme changes, and 2 GTK applications (Firefox (GTK3) and LACT (GTK4)) displaying the issue. STEPS TO REPRODUCE 1. Launch a GTK application, e.g. Firefox with theme set to "system theme - auto" 2. Confirm that the application's theme is in sync with system theme 3. In System Settings change the theme between light and dark OBSERVED RESULT On the first theme change, GTK applications stay in their previous mode. On each subsequent theme change, GTK applications also change their theme, but to the opposite of the system theme. EXPECTED RESULT GTK applications consistently follow system theme. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Arch Linux KDE Plasma Version: 6.6.0 KDE Frameworks Version: 6.23.0 Qt Version: 6.10.2 ADDITIONAL INFORMATION The issue started appearing after upgrading Plasma from 6.5.5 to 6.6.0. On Plasma 6.5 GTK applications correctly followed system theme.
Can confirm. A pretty bizarre issue.
gedit reacts to theme changes as expected though. Is FF the only app that misbehaves?
Created attachment 189824 [details] light/dark gtk issue
i can also confirme the bug on fedora 43. see the light/dark gtk issue attachment
A possibly relevant merge request was started @ https://invent.kde.org/plasma/xdg-desktop-portal-kde/-/merge_requests/523
Git commit b5dc335c40eb6c49de0736ea1d42c4bfa0c98b7c by Nicolas Fella. Committed on 19/02/2026 at 16:30. Pushed by vladz into branch 'master'. Revert "settings: use stylehints instead of manually determining dark vs light" This causes the change signal to be emitted with the old value This reverts commit 1d5e30d155b4e727f7ae2cc0693ac3dced7ded16. M +11 -9 src/settings.cpp https://invent.kde.org/plasma/xdg-desktop-portal-kde/-/commit/b5dc335c40eb6c49de0736ea1d42c4bfa0c98b7c
Git commit b8479f2aca2e2cdc392f44d05a1a8abf26f2ad4d by Vlad Zahorodnii. Committed on 19/02/2026 at 17:55. Pushed by vladz into branch 'Plasma/6.6'. Revert "settings: use stylehints instead of manually determining dark vs light" This causes the change signal to be emitted with the old value This reverts commit 1d5e30d155b4e727f7ae2cc0693ac3dced7ded16. (cherry picked from commit b5dc335c40eb6c49de0736ea1d42c4bfa0c98b7c) Co-authored-by: Nicolas Fella <nicolas.fella@gmx.de> M +11 -9 src/settings.cpp https://invent.kde.org/plasma/xdg-desktop-portal-kde/-/commit/b8479f2aca2e2cdc392f44d05a1a8abf26f2ad4d
Confirming the above change fixes the issue. Thank you!