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You can set up QT to use GTK themes (seems like this is the default in KDE Plasma): https://wiki.archlinux.org/index.php/Uniform_look_for_Qt_and... I currently just don't have any QT based apps on my Arch system though I don't think.
I came at it the other way - make GTK apps look like Qt ones. Everything on my system uses Breeze Dark. The only way I can tell GTK programs from Qt ones is the "About" dialog, or the file picker. (Oh, how I wish I could use the Qt file picker in GTK programs) (edit: QT -> Qt. Seasons greetings to the flagkilled throwaway who informed me of my mistake.)
QT means QuickTime.