I tried installing the current Kdenlive package from Parabola repos and it requires rttr as well

sudo pacman -S kdenlive
resolving dependencies...
warning: cannot resolve "rttr", a dependency of "kdenlive" 
:: The following package cannot be upgraded due to unresolvable dependencies:
      kdenlive

From my understanding internet access is blocked within the build() function.

If you try to build Kdenlive without the rttr library installed, it will try to download and compile rttr itself. But since the internet connection is blocked, it will refuse to build properly without the rttr package.

I'm not sure if there are certain exceptions that apply to this, I thought it would be appropriate to add a separate rttr package.

ok sry i must already have that package installed

$ LANG=C pacman -Si kdenlive | grep Depends
Depends On      : qt5-networkauth  knewstuff  knotifyconfig  kfilemetadata  purpose  mlt6  rttr  breeze-icons  frei0r-plugins

what that usually means, is that 'kdenlive' needs a rebuild or upgrade - if arch removed the 'rttr' package, it is because it is not needed

also, the arch package no longer links to webengine; so strinctly speaking, kdenlive could be removed from the blacklist

If you try to build Kdenlive without the rttr library installed, it will try to download and compile rttr itself.

... but if that's the case, then we would want to keep 'kdenlive' on the blacklist and package 'rttr'