Currently, my log contains the warning:
file:///usr/share/plasma/wallpapers/org.kde.slideshow/contents/ui/main.qml:63: TypeError: Property 'setAction' of object ScreenLocker::WallpaperIntegration(0x5602870c3910) is not a function
And indeed, the WallpaperIntegration class in KScreenLocker does not contain such a function. Removing the calls to setAction fixes the warning but I'm not entirely sure if this is actually a regression that should be fixed by replacing the calls to setAction by something else. Any guidance here would be appreciated.
I tried to do more investigation but I end up at the start of the history of the plasma-workspace and kscreenlocker repositories so I don't know if there's any more git blame delving I can do here.