[Joel_Mckay]

Note Qt5 is currently broken in some universe MATE desktop repos.

wxwidgets would likely be cleaner to maintain over the long-term, and seems more stable for event callbacks etc.

I'll admit some users like spelunking environment variables like QT_QPA_PLATFORM, and application specific python3-venv installs...

Sometimes a web SPA is just easier to avoid the whole mess of porting. =3

[anthk]

Install qt5ct and set

      #!/bin/sh
      export QT_QPA_PLATFORMTHEME=qt5ct 

at /etc/profile.d/qt5.sh with 0755 perms.

[Joel_Mckay]

In some situations qt5ct was the problem at certain points in the past. In this case that trick won't work either.

The Cinnamon desktop package is functional in 24.04 LTS for "reasons" yet to be identified.

Thanks for trying to help though =3

[anthk]

OFC with qt5ct it's suggested to add the qgtk styles too. For instance, the GTK2/3 one to map your GTK2/3 (and 4) settings into the QT5 widgets.

BTW, to enforce Zukitre as the GTK4 theme with Elementary icons:

create /etc/profile.d/gtk.sh

       #!/bin/sh 
       export GTK_THEME=Zukitre
       export GTK_ICON_THEME=Elementary

And, yes, Zuki themes and the Elementary icon set must be installed too.

[Joel_Mckay]

The theme overrides were not working, so the issue is likely in how the Qt5 template layer was built/integrated in the universe MATE build (Qt6ct seems unaffected, but will not help with code built on Qt5). i.e. the applications may not crash, but will look garbled and exhibit undefined GUI behaviors on legacy desktops. Overriding the themes and other documented workarounds will only suppress standard warnings, but have not had any impact on the core Qt5 issues.

For an LTS OS intended to be around for 12 years, I am not sure things have turned out well in user space and Qt5.

Hopefully, this saves someone a few hours of chasing this external issue in their own projects. =3

[anthk]

Uhm, I use Mate under Trisquel 11 (bound to Ubuntu 22 releases, but libre), it's the default desktop DE and I have no issues with neither qt5ct nor GTK theme overriding, which is more apt for Gnome3/OSTree based desktops than normal setups.

[Joel_Mckay]

This issue appeared in Canonical's Ubuntu 24.04.1 Noble Numbat MATE Desktop iso and universe repository meta packages ubuntu-mate-desktop and mate-desktop .

The meta package ubuntucinnamon-desktop does not seem to impact the Qt5 Apps/installation in a detrimental way.

If I could offer any advice about this mystery issue... probably wiser to defer upgrading for a bit =3

[jcelerier]

Why qt5ct when qt6 (and qt6ct) were released years ago, in 2020 ?

[doubled112]

Same reason as usual. Not every application has been ported.