I am running KDE on Kubuntu 25.04. When I set QT_QPA_PLATFORMTHEME=qt6ct my KDE system settings font sizes are overriden apart from the themes. When I don’t set it, the font sizes in QT applications do not match the KDE system font settings. What should I do to have uniform settings between KDE and QT applications, preferably applying KDE settings on QT apps?
There is no distinction between “KDE applications” and “Qt applications”, KDE settings should apply to all Qt applications. Can you give an example of what you mean by a “Qt application”?
Do not use qt6ct with KDE. KDE has its own platform theme provided through the plasma-integration package. qt6ct destroys this integration.
Where can I find the settings for this?
I am using GNU Radio. I am using Ubuntu Font in KDE system settings. The fonts in GNU Radio is much thinner which might suggest a difference in the font weight.
So your question is about Qt6 vs Qt5 applications, not about “KDE vs Qt”. To make Plasma settings apply to Qt5 applications you need the Qt5 version of plasma-integration installed.
No. It is about KDE vs QT. The font settings in KDE system settings especially the font width does not translate into QT. All KDE apps such as Konsole have the right font settings applied.
Please note that I have force set the font DPI in the KDE Font system settings. Should I uncheck it and just use the font scaling slider?
Again: there is no technical difference whatsoever between “KDE apps” and “Qt apps”, so it is just impossible that settings apply only to one of them. And, since the only example you gave of what you call “Qt app” is a Qt 5 application, the most likely cause of the difference is that settings are not being applied to Qt 5 apps.
System settings > Colors and themes
System settings > Text and fonts
It does not change my situation unfortunately. Situation is same as shared in the screenshot above.
That’s because you need to get rid of that `QT_QPA_PLATFORMTHEME=qt6ct` and let plasma-integration do its job. Why are you deliberately breaking KDE and asking in this forum
Perhaps I was not clear, QT_QPA_PLATFORMTHEME=qt6ct is removed already and the snapshot was taken. The snapshot with font differences is with this variable setting removed.
As arojas said, install the Qt5 version of plasma-integration. On Ubuntu 25.04 that would be plasma5-integration.
The reason why most of your KDE and Qt applications follow a certain theme but GNU Radio does not is because those KDE and Qt applications are based on Qt6 and follow the Qt6 version of plasma-integration that already comes installed on your system, while GNU Radio is a Qt5 application and will only follow plasma5-integration, which you do not have installed.
This should be the cause for the theme difference on your system. The fact that you were using qt6ct was just an additional factor in the confusion, because forcing your system to use qt6ct makes your whole system ignore the theme you set in System Settings (that is to say, don’t use qt6ct on Plasma).
The moment you install plasma5-integration then GNU Radio should use the theme set by you in System Settings. It might require a logout and login or reboot after you install it.
@Herzenschein : plasma5-integration is already installed. [installed, automatic]. Yes, I have rebooted etc.
Is this not just how python applications look in Qt? I use Picard for music tagging and it’s never looked “right” in KDE. But I’ve always just put it down to it being a Qt Python app.
How did you install gnuradio? Is it natively installed, or is it a flatpak/snap thing?
@arojas : It is native installation.
apt search gnuradio
gnuradio/plucky,now 3.10.11.0-2build4 amd64 [installed,automatic]
GNU Radio Software Radio Toolkit