If I change global theme from Breeze Light to Breeze Dark, only Firefox and Thunderbird change to a dark theme but not the Breeze one, both switch to Dark Adwaita (even if in Application Style > GTK settings I see Breeze applied), other GTK apps like UGet and Pamac don’t update their theme and sometimes even after restarting them they remain using Light Breeze, the only solution I found in that special case is to change Color scheme to Breeze Light then switch to Breeze Dark (sometimes needed to be done two times) which seems to fix Pamac and UGet and force them to use Breeze Dark theme.
According to someone from KDE team, it seems to be a problem related to packaging distribution, and it doesn’t happen on latest KDE Neon neither latest Fedora KDE.
https://bugs.kde.org/show_bug.cgi?id=421745
I tried Arch tips to unify both Qt and GTK apps, so I installed gnome-settings-daemon, gsettings-desktop-schemas and gsettings-qt but the same problem remains. Is there any GTK background service that needs to be started to sync Plasma applied theme to GTK+ apps ?
What you are looking for may be the xsettingsd package
man xsettingsd
Online manual xsettingsd(1) — Arch manual pages
I forget to mention this problem is specific to Wayland and not X11.
I cannot understand your original topic - please split it into logical paragraphs - now it is just a wall of text.
On Plasma Wayland, if you set a global theme, then all running GTK+ apps will not be updated with that theme, and you need to restart them to get it working.
I’m not sure if it’s a problem related to Arch based distro, because they claim setting a global theme works fine for running GTK+ apps on other distros like KDE Neon and Fedora KDE.
What I found is that by simply restarting a background service that uses GSettings for Wayland, the theme can be applied on running GTK+ apps without needing to restart them.
When you change theme n the settings manager a message is broadcasted on dbus and the new settings is written to various files or folders in .config.
If the app - for some reason - is not picking up the message - it will require the app to be reloaded or the broadcasting daemon reloaded.
The interaction between toolkits - in this case Qt and Gtk - has been an issue for decades.
It is getting better but it appears to me - on a personal opinion - the zen which Gnome developer strive for - is creating obstacles for those KDE developers trying to make it possible to create visually coherency.
I think some packages are missing on Manjaro to force the reloading of that service, are gnome-settings-daemon, gsettings-desktop-schemas and gsettings-qt not needed for Manjaro KDE to get uniform look between Qt and GTK+ apps ? Uniform look for Qt and GTK applications - ArchWiki