This seems to be the issue, there’s been another user that brought it to attention in another thread some time ago. Seems that a required package has been removed from the official repos (kdebase-runtime) while some of the packages depend on it, this is largely an upstream packaging issue that should be resolved eventually.
I just installed Kdenlive and while it runs I got a warning that functionality will be restricted due to missing dependencies. The Breeze icons and default theme are also missing.
Sounds like your are trying to mix K-apps in a non Plasma/KDE environment. Have you installed all the dependencies?
Likely not as I’m used to debian/ubuntu setups. I will go search and discover
nice catch @Dobbie03.
The arch packages kdenlive page entry shows (along with other dependencies);
plasma-desktop (optional) - theme configuration
so the kdenlive devs aren’t strict on making you install all of kde if you want to use their package… nice! Maybe I’ll download it as I’ve used it before and it’s a toss up between that and blender <3