After kde-config-gtk-style and kde-config-gtk-style-preview have been upgraded to version 4:5.27.12-0ubuntu0.1, UI scaling ratio that is set in KDE System Settings is no longer applied to GTK applications. For example, Thunderbird UI is not scaled and looks too small on my display. I have UI scaling set to 162.5% in System Settings -> Display Configuration. This scaling ratio applies to KDE applications.
Rolling back kde-config-gtk-style and kde-config-gtk-style-preview to 4:5.27.11-0ubuntu2 restores proper scaling in GTK applications.
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: kde-config-gtk-style 4:5.27.12-0ubuntu0.1
ProcVersionSignature: Ubuntu 6.8.0-52.53.1-lowlatency 6.8.12
Uname: Linux 6.8.0-52-lowlatency x86_64
ApportVersion: 2.28.1-0ubuntu3.3
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Fri Feb 7 04:55:10 2025
InstallationDate: Installed on 2015-05-01 (3569 days ago)
InstallationMedia: Kubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: kde-gtk-config
UpgradeStatus: Upgraded to noble on 2024-09-05 (155 days ago)
This is the result of upstream KDE reverting a change 1st made on 5.27.11 in how the GTK scaling factor is calculated. The now current method (from this update) remains the default all the way up to the latest plasma 6.3. These kinds of changes are always going to have cases where some people are negatively affected. Sorry that this seems to be the case here.
We will actively monitor any further reports/