HiDPI is broken on KDE Wayland

[martymarty004]

Hello, I’m using the default installation of LibreOffice on Fedora 42 KDE with two displays.
On the secondary monitor the application renders perfectly, but on the primary one the GUI is way too small to be used.

(Image) UI on primary display

(Image) UI on secondary display

I tried changing the icon size in Settings / LibreOffice / View, but it does almost nothing.
The icon theme is the default Breeze (Dark) from KDE.

The only workaround I found to solve the issue was on this website, which basically tells you to ditch Wayland and run the program under X11 by setting the environment variable QT_QPA_PLATFORM=xcb before starting it.
(I put this directly into the .desktop file, so it just works if I open it from the launcher or by opening a file).

I didn’t see many similar threads regarding this issue, has it been fixed in some more recent version? Or is there something wrong with my current configuration?

Any help is appreciated.

System Info

Display 1: 2560x1440p@144Hz - 27’’ - Scale 115%
Display 2: 1920x1080p@60Hz - 24’’ - Scale 100%

Kernel: Linux 6.16.3-200.fc42.x86_64
GPU: GeForce RTX 4070 - Proprietary driver 575.64.05
KDE: Plasma 6.4.4 (Wayland) - Qt 6.9.1

LibreOffice Info

Version: 25.2.5.2* (X86_64)
Build ID: 520(Build:2)
CPU threads: 24; OS: Linux 6.16; UI render: default; VCL: kf6 (cairo+wayland)
Locale: it-IT (it_IT.UTF-8); UI: it-IT
Calc: threaded

(*latest version in the official Fedora Updates repository)

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EDIT: Added screenshot of secondary display for reference

[mariosv]

Please take a look at tdf#163648

[martymarty004]

I see this has been a longstanding issue.

I tried the environment variables that were suggested on the thread you linked, but launching using GTK3 with SAL_USE_VCLPLUGIN=gtk3 of course makes the program render without all KDE theming, which I’d prefer to keep.

Furthermore, I also tried the second option, but if I force the scaling with SAL_USE_VCLPLUGIN=qt6 QT_SCALE_FACTOR=2, the problem becomes even more noticeable. The UI proportions between menus / icons are completely broken, and if I try to move the window across monitors everything becomes huge:

Primary display

Secondary display

(Note that LibreOffice Calc was full-screen when I took the screenshot)

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Since launching with X11 seems to solve all the scaling issues, I will probably keep using this workaround for now, until the bug gets fixed in a future version or until Fedora decides to drop X11 support altogether.

The only thing I don’t understand is how there seems to be only a few people facing this problem and reporting it, since apparently the only requirement to reproduce the bug is running KDE on Wayland with a multi-monitor setup.