Hey guys,
just have a quick question. I just set up CachyOS for the first time (coming from gentoo) and noticed that Qt apps are not matching with the dark Gnome color scheme - they’re all white and stuff. How do I switch to a dark theme (OLED display)? I tried using Kvantum and the KDE settings (even installed Plasma Meta o.O), switched to ‘Breeze Dark’, but it didn’t set for the Qt apps, ya know? So, what’s the deal?
Thanks a bunch in advance 
Take a look at these two articles:
https://wiki.archlinux.org/title/Environment_variables#Per_Wayland_session
You need to install a few packages, if you don’t need qt5 you can skip the qt5 ones, but I have installed all of them since I don’t know how to tell if the app is qt5:
kvantum kvantum-qt5 kvantum-theme-libadwaita-git qt5ct qt6ct qt6-wayland qt5-wayland
If you use wayland, add to your ~/.config/environment.d/envvars.conf:
QT_QPA_PLATFORM=wayland
QT_QPA_PLATFORMTHEME=qt5ct
If you use x11: GitHub - desktop-app/qt5ct: Mirror of the Qt5 Configuration Tool repository
Restart.
Run kvantummanager to select the theme you want, I used libadwaita. Run qt5ct and maybe qt6ct too to select kvantum.
If you need theming for a root password app, you need to do these things for your root account too (didn’t try it).