Update to 26.05: QQmlApplicationEngine / KDE Kirigami issues

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1

Context

After i updated (and rebuilt) the nixpkgs.url from 25.11 (plasma6) to 26.05 (plasma6) I first noticed the fonts not displaying on gtk apps, such as GNU Gimp and protonvpn-app (gui).

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Then when i tried to access the font manager through system settings crash handler threw an error:

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Here i executed the system settings app via terminal:

↪ systemsettings 
QQmlComponent: Component is not ready
"qrc:/qt/qml/org/kde/systemsettings/Main.qml:38:5: Type SideBarItem unavailable"
"qrc:/qt/qml/org/kde/systemsettings/SideBarItem.qml:12:1: Kirigami.ApplicationItem is not a type"
Fatal error while loading the sidebar view qml component
KCrash: Application '.systemsettings-wrapped' crashing... crashRecursionCounter = 2
fish: Job 1, 'systemsettings' terminated by signal SIGABRT (Abort)
2

Please do not cross post in multiple places without references.

This question has been asked in at least one Nico’s discord as well.

For public visibility and searchability I’d prefer to continue the discussion here.

Therefore I will repeat the question I asked over in the discord:

Did you reboot after the update?

3

Hey. Yeah, sorry i forgot to reference. I did reboot right after rebuild finished, but the problem was there until i deleted the caches from nix store and rebooted (shutdown, pw-on)

This issue is solved. I think the gtk font is an another issue i should look into myself.